feat(workspaces): Win8 Start-style tile-grid home page

Rebuild the workspace home as a Windows 8 Start-screen-style tile grid,
replacing the max-w-3xl vertical card list.

Pure core (zero DOM/Svelte/fetch, fully unit-tested):
- logic/tile-layout.ts — geometryFor(width, height) resolves WIDE (4 fixed
  ~120px rows, column-wise flow, 4x2 span cap) or TALL (2 fixed columns,
  row-wise flow, 2x2 cap); pack() is the ONLY order->coordinates transform
  (greedy first-fit in fill order, hole-free, render-clamped per geometry);
  firstEmptySlot/insertAtFirstEmptySlot/mergeLayout/resizeTile/moveTile/
  sortByRecentActivity/sanitizeLayout. Persisted data is
  orientation-independent {version:1, tiles:[{id,colSpan,rowSpan,order}]} —
  order + spans only, never positions; the same data renders in either
  geometry (spans clamp for the render, persisted values untouched).
- logic/drag-controller.ts — pure pointer/press state machine: mouse
  threshold-drag + tap-open; touch long-press lifts + selects, pre-lift
  movement cancels so vertical scrolling never fights the gesture.

Shell:
- tile-layout-store.svelte.ts — thin reactive wrapper persisting through
  the injected createLocalStore adapter (dispatch.workspaces.tiles), ops:
  sync/resize/move/placeFirstEmpty/sortByRecentActivity.
- ui/HomeTileGrid.svelte — CSS-grid tile canvas (wide: horizontal scroll +
  snap + wheel pan + pan arrow + scroll indicator; tall: native vertical
  scroll), FLIP-animated reflow, drag ghost, transient resize preview.
- ui/HomeHeader.svelte — fixed chrome: Dispatch display title, New
  workspace popover (same slug validation; creates via create-on-miss and
  does NOT navigate — the new tile lands in the first empty slot in fill
  order and enters rename mode), global Plugins button, sort-by-recent
  overflow; compact icon buttons + bottom sheet on tall screens.
- ui/WorkspaceTile.svelte — tile face (title, /slug, conversation count,
  relative last-activity, live active dots, starred tint); inline rename
  with the old card's semantics.
- ui/TileActionBar.svelte — slides up on select (right-click / long-press):
  Open, Rename, Resize, Star/Unstar, Details, Plugins, Delete (old confirm
  + store call preserved).
- ui/ResizePicker.svelte — Word-style insert-table hover grid (wide 4x2 /
  tall 2x2) with arrow/Enter/Escape support and ghost preview on commit.
- ui/WorkspaceDetails.svelte — flyout holding the old card's default-cwd
  input + default-computer select (same store calls + error states).
- WorkspacesHome.svelte orchestrates; App.svelte untouched (same props).
- WorkspaceCard.svelte is removed (replaced by the tile system).

Manual tile order rules; starred workspaces get a tint (star is no longer
a sort key); workspaces unknown to the layout append at the end.

vitest: jsdom gains PointerEvent (MouseEvent-based) + Element.animate
stubs — the pointer logic is the outermost edge for the drag tests.

Verification: svelte-check 0/0, vitest 1655 passed (102 files, twice),
biome clean, vite build OK.

1 files changed, 180 insertions, 0 deletions

diff --git a/src/features/workspaces/ui/HomeTileGrid.test.ts b/src/features/workspaces/ui/HomeTileGrid.test.ts
new file mode 100644
index 0000000..3229d4e
--- /dev/null
+++ b/src/features/workspaces/ui/HomeTileGrid.test.ts
@@ -0,0 +1,180 @@
+import type { WorkspaceEntry } from "@dispatch/wire";
+import { fireEvent, render, screen } from "@testing-library/svelte";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { geometryFor, type Placement } from "../logic/tile-layout";
+import type { WorkspaceStore } from "../store.svelte";
+import HomeTileGrid from "./HomeTileGrid.svelte";
+
+const WIDE = geometryFor(1920, 1080);
+
+function ws(overrides: Partial<WorkspaceEntry> = {}): WorkspaceEntry {
+  return {
+    id: "a",
+    title: "Workspace A",
+    defaultCwd: null,
+    defaultComputerId: null,
+    starred: false,
+    createdAt: 1,
+    lastActivityAt: 2,
+    conversationCount: 1,
+    ...overrides,
+  };
+}
+
+function placement(id: string, col: number, row: number): Placement {
+  return { id, col, row, colSpan: 1, rowSpan: 1 };
+}
+
+function fakeStore(): WorkspaceStore {
+  return {
+    rename: vi.fn(),
+  } as unknown as WorkspaceStore;
+}
+
+function baseProps() {
+  return {
+    geometry: WIDE,
+    workspacesById: new Map([
+      ["a", ws()],
+      ["b", ws({ id: "b", title: "Workspace B" })],
+    ]),
+    store: fakeStore(),
+    onOpen: vi.fn(),
+    onSelect: vi.fn(),
+    onReorder: vi.fn(),
+    onRenameEnd: vi.fn(),
+  };
+}
+
+describe("HomeTileGrid", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("renders one tile per placement, positioned by the packed spans", () => {
+    const props = baseProps();
+    const { container } = render(HomeTileGrid, {
+      props: {
+        ...props,
+        placements: [placement("a", 1, 1), placement("b", 2, 1)],
+      },
+    });
+
+    expect(screen.getByRole("button", { name: "Open workspace Workspace A" })).toBeInTheDocument();
+    expect(screen.getByRole("button", { name: "Open workspace Workspace B" })).toBeInTheDocument();
+    const wrappers = container.querySelectorAll("[data-tile-id]");
+    expect(wrappers).toHaveLength(2);
+    expect(wrappers[0]?.getAttribute("style")).toContain("grid-column: 1 / span 1");
+    expect(wrappers[1]?.getAttribute("style")).toContain("grid-column: 2 / span 1");
+  });
+
+  it("a tap (press + release without moving) opens the workspace", async () => {
+    const props = baseProps();
+    render(HomeTileGrid, {
+      props: { ...props, placements: [placement("a", 1, 1)] },
+    });
+
+    const wrapper = screen.getByRole("button", { name: "Open workspace Workspace A" });
+    fireEvent.pointerDown(wrapper, { button: 0, clientX: 10, clientY: 10, pointerType: "mouse" });
+    fireEvent.pointerUp(wrapper);
+
+    expect(props.onOpen).toHaveBeenCalledWith("a");
+    expect(props.onSelect).not.toHaveBeenCalled();
+  });
+
+  it("right-click selects the tile", async () => {
+    const props = baseProps();
+    render(HomeTileGrid, {
+      props: { ...props, placements: [placement("a", 1, 1)] },
+    });
+
+    const wrapper = screen.getByRole("button", { name: "Open workspace Workspace A" });
+    fireEvent.contextMenu(wrapper);
+
+    expect(props.onSelect).toHaveBeenCalledWith("a");
+    expect(props.onOpen).not.toHaveBeenCalled();
+  });
+
+  it("dragging shows the transient ghost, and dropping reorders (when over a target)", async () => {
+    const props = baseProps();
+    const { container } = render(HomeTileGrid, {
+      props: { ...props, placements: [placement("a", 1, 1), placement("b", 2, 1)] },
+    });
+
+    const wrapper = screen.getByRole("button", { name: "Open workspace Workspace A" });
+    // jsdom has no elementFromPoint hit-testing → targetIndex stays -1 (no-op),
+    // but the GHOST must appear while dragging and disappear on drop.
+    Object.defineProperty(document, "elementFromPoint", {
+      configurable: true,
+      value: () => null,
+    });
+    fireEvent.pointerDown(wrapper, { button: 0, clientX: 10, clientY: 10, pointerType: "mouse" });
+    fireEvent.pointerMove(wrapper, { clientX: 80, clientY: 40 });
+
+    expect(container.querySelector(".pointer-events-none.fixed")).not.toBeNull();
+
+    fireEvent.pointerUp(wrapper);
+    expect(container.querySelector(".pointer-events-none.fixed")).toBeNull();
+    // No hit target → no reorder call.
+    expect(props.onReorder).not.toHaveBeenCalled();
+    // And no navigation either (a drag is not a tap).
+    expect(props.onOpen).not.toHaveBeenCalled();
+  });
+
+  it("a touch long-press lifts the tile and selects it (never opens)", async () => {
+    const props = baseProps();
+    render(HomeTileGrid, {
+      props: { ...props, placements: [placement("a", 1, 1)] },
+    });
+
+    const wrapper = screen.getByRole("button", { name: "Open workspace Workspace A" });
+    fireEvent.pointerDown(wrapper, {
+      button: 0,
+      clientX: 10,
+      clientY: 10,
+      pointerType: "touch",
+    });
+    await vi.advanceTimersByTimeAsync(500);
+
+    expect(props.onSelect).toHaveBeenCalledWith("a");
+    expect(props.onOpen).not.toHaveBeenCalled();
+  });
+
+  it("a touch drag that moves before the long-press cancels (scroll wins)", async () => {
+    const props = baseProps();
+    render(HomeTileGrid, {
+      props: { ...props, placements: [placement("a", 1, 1)] },
+    });
+
+    const wrapper = screen.getByRole("button", { name: "Open workspace Workspace A" });
+    fireEvent.pointerDown(wrapper, {
+      button: 0,
+      clientX: 10,
+      clientY: 10,
+      pointerType: "touch",
+    });
+    fireEvent.pointerMove(wrapper, { clientX: 10, clientY: 120 });
+    await vi.advanceTimersByTimeAsync(500);
+
+    expect(props.onSelect).not.toHaveBeenCalled();
+    expect(props.onOpen).not.toHaveBeenCalled();
+  });
+
+  it("previews a transient span for the resizing tile", () => {
+    const props = baseProps();
+    const { container } = render(HomeTileGrid, {
+      props: {
+        ...props,
+        placements: [placement("a", 1, 1)],
+        preview: { id: "a", colSpan: 3, rowSpan: 2 },
+      },
+    });
+
+    const wrapper = container.querySelector("[data-tile-id='a']");
+    expect(wrapper?.getAttribute("style")).toContain("span 3");
+    expect(wrapper?.getAttribute("style")).toContain("span 2");
+  });
+});