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, 157 insertions, 0 deletions

diff --git a/src/features/workspaces/ui/WorkspaceTile.test.ts b/src/features/workspaces/ui/WorkspaceTile.test.ts
new file mode 100644
index 0000000..918aa1c
--- /dev/null
+++ b/src/features/workspaces/ui/WorkspaceTile.test.ts
@@ -0,0 +1,157 @@
+import type { WorkspaceEntry } from "@dispatch/wire";
+import { render, screen } from "@testing-library/svelte";
+import userEvent from "@testing-library/user-event";
+import { describe, expect, it, vi } from "vitest";
+import type { WorkspaceResult } from "../adapter/http";
+import type { Placement } from "../logic/tile-layout";
+import type { WorkspaceStore } from "../store.svelte";
+import WorkspaceTile from "./WorkspaceTile.svelte";
+
+function fakeEntry(overrides: Partial<WorkspaceEntry> = {}): WorkspaceEntry {
+  return {
+    id: "my-ws",
+    title: "My Workspace",
+    defaultCwd: null,
+    defaultComputerId: null,
+    starred: false,
+    createdAt: 1,
+    lastActivityAt: Date.now() - 90_000, // "1m" relative time
+    conversationCount: 3,
+    ...overrides,
+  };
+}
+
+function fakeStore(): WorkspaceStore {
+  return {
+    rename: vi.fn(
+      async (id: string, title: string): Promise<WorkspaceResult<WorkspaceEntry>> => ({
+        ok: true,
+        value: fakeEntry({ id, title }),
+      }),
+    ),
+  } as unknown as WorkspaceStore;
+}
+
+function fakePlacement(overrides: Partial<Placement> = {}): Placement {
+  return { id: "my-ws", col: 1, row: 1, colSpan: 1, rowSpan: 1, ...overrides };
+}
+
+describe("WorkspaceTile", () => {
+  it("renders the title, slug, conversation count, and relative last-activity", () => {
+    render(WorkspaceTile, {
+      props: {
+        ws: fakeEntry(),
+        store: fakeStore(),
+        placement: fakePlacement(),
+        onRenameEnd: () => {},
+      },
+    });
+    expect(screen.getByText("My Workspace")).toBeInTheDocument();
+    expect(screen.getByText("/my-ws")).toBeInTheDocument();
+    expect(screen.getByText(/3 conversations/)).toBeInTheDocument();
+    expect(screen.getByText("1m")).toBeInTheDocument();
+  });
+
+  it("shows the active indicator only when the active port says so", async () => {
+    const { container, rerender } = render(WorkspaceTile, {
+      props: {
+        ws: fakeEntry(),
+        store: fakeStore(),
+        placement: fakePlacement(),
+        active: true,
+        onRenameEnd: () => {},
+      },
+    });
+    expect(
+      container.querySelector('[aria-label="Workspace has active conversations"]'),
+    ).not.toBeNull();
+
+    await rerender({
+      ws: fakeEntry(),
+      store: fakeStore(),
+      placement: fakePlacement(),
+      active: false,
+      onRenameEnd: () => {},
+    });
+    expect(container.querySelector('[aria-label="Workspace has active conversations"]')).toBeNull();
+  });
+
+  it("double-clicking the title reveals the rename input (semantics preserved)", async () => {
+    const user = userEvent.setup();
+    const store = fakeStore();
+    render(WorkspaceTile, {
+      props: {
+        ws: fakeEntry(),
+        store,
+        placement: fakePlacement(),
+        onRenameEnd: () => {},
+      },
+    });
+
+    await user.dblClick(screen.getByText("My Workspace"));
+    expect(screen.getByLabelText("Workspace title")).toHaveValue("My Workspace");
+  });
+
+  it("the parent-driven rename mode (action bar) opens the same inline editor", async () => {
+    const user = userEvent.setup();
+    const store = fakeStore();
+    render(WorkspaceTile, {
+      props: {
+        ws: fakeEntry(),
+        store,
+        placement: fakePlacement(),
+        renaming: true,
+        onRenameEnd: () => {},
+      },
+    });
+    const input = screen.getByLabelText("Workspace title");
+    expect(input).toHaveValue("My Workspace");
+
+    await user.clear(input);
+    await user.type(input, "Renamed{Enter}");
+    expect(store.rename).toHaveBeenCalledWith("my-ws", "Renamed");
+  });
+
+  it("a failed rename surfaces the error on the face", async () => {
+    const user = userEvent.setup();
+    const store = {
+      rename: vi.fn(
+        async (): Promise<WorkspaceResult<WorkspaceEntry>> => ({
+          ok: false,
+          error: "boom",
+        }),
+      ),
+    } as unknown as WorkspaceStore;
+    render(WorkspaceTile, {
+      props: {
+        ws: fakeEntry(),
+        store,
+        placement: fakePlacement(),
+        renaming: true,
+        onRenameEnd: () => {},
+      },
+    });
+
+    await user.type(screen.getByLabelText("Workspace title"), "x{Enter}");
+    expect(screen.getByText("boom")).toBeInTheDocument();
+  });
+
+  it("an unchanged title does not hit the store and still ends the session", async () => {
+    const user = userEvent.setup();
+    const store = fakeStore();
+    const onRenameEnd = vi.fn();
+    render(WorkspaceTile, {
+      props: {
+        ws: fakeEntry(),
+        store,
+        placement: fakePlacement(),
+        renaming: true,
+        onRenameEnd,
+      },
+    });
+
+    await user.type(screen.getByLabelText("Workspace title"), "{Enter}");
+    expect(store.rename).not.toHaveBeenCalled();
+    expect(onRenameEnd).toHaveBeenCalled();
+  });
+});