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, 109 insertions, 0 deletions

diff --git a/src/features/workspaces/ui/WorkspaceTile.svelte b/src/features/workspaces/ui/WorkspaceTile.svelte
new file mode 100644
index 0000000..4059690
--- /dev/null
+++ b/src/features/workspaces/ui/WorkspaceTile.svelte
@@ -0,0 +1,109 @@
+<script lang="ts">
+  import type { WorkspaceEntry } from "@dispatch/wire";
+  import type { WorkspaceStore } from "../store.svelte";
+  import { relativeTime } from "../logic/view-model";
+  import type { Placement } from "../logic/tile-layout";
+
+  let {
+    ws,
+    store,
+    placement,
+    selected = false,
+    renaming = false,
+    active = false,
+    onRenameEnd,
+  }: {
+    ws: WorkspaceEntry;
+    store: WorkspaceStore;
+    /** The tile's resolved footprint (already preview-adjusted by the grid). */
+    placement: Placement;
+    selected?: boolean;
+    /** The parent-driven rename mode (the action bar's Rename action). */
+    renaming?: boolean;
+    /** At least one conversation in this workspace is generating/queued. */
+    active?: boolean;
+    /** The tile finished its rename session (saved or cancelled). */
+    onRenameEnd: () => void;
+  } = $props();
+
+  // ── Title: double-click to rename inline (semantics preserved from the
+  // WorkspaceCard), or enter via the action bar's Rename action (`renaming`).
+  let editing = $state(false);
+  let titleDraft = $state("");
+  let titleInput = $state<HTMLInputElement | undefined>();
+  let titleError = $state<string | null>(null);
+
+  function startEdit(): void {
+    titleDraft = ws.title;
+    titleError = null;
+    editing = true;
+    queueMicrotask(() => titleInput?.focus());
+  }
+
+  // Seed (only) when the parent-driven rename mode turns on.
+  $effect(() => {
+    if (renaming) startEdit();
+  });
+
+  async function saveTitle(): Promise<void> {
+    if (!editing) return;
+    const title = titleDraft.trim();
+    editing = false;
+    onRenameEnd();
+    if (title === "" || title === ws.title) return;
+    const result = await store.rename(ws.id, title);
+    if (!result.ok) titleError = result.error;
+  }
+
+  function cancelTitle(): void {
+    editing = false;
+    titleError = null;
+    onRenameEnd();
+  }
+
+  // The face's semantic key (tests read it).
+  const faceKey = $derived(`tile-${placement.id}`);
+</script>
+
+<div data-tile-face={faceKey} class="flex h-full w-full flex-col gap-1 p-3">
+  {#if editing}
+    <input
+      bind:this={titleInput}
+      bind:value={titleDraft}
+      class="input input-bordered input-sm"
+      aria-label="Workspace title"
+      onkeydown={(e) => {
+        if (e.key === "Enter") void saveTitle();
+        else if (e.key === "Escape") cancelTitle();
+      }}
+      onblur={() => void saveTitle()}
+    />
+  {:else}
+    <!-- svelte-ignore a11y_no_static_element_interactions, a11y_click_events_have_key_events -->
+    <span
+      class="line-clamp-2 cursor-default text-lg leading-tight font-bold"
+      title="Double-click to rename"
+      ondblclick={startEdit}>{ws.title}</span
+    >
+  {/if}
+
+  <span class="font-mono text-xs opacity-50">/{ws.id}</span>
+
+  {#if titleError}
+    <p class="text-xs text-error">{titleError}</p>
+  {/if}
+
+  <div class="mt-auto flex items-center gap-2 text-xs opacity-80">
+    {#if active}
+      <span
+        class="loading loading-dots loading-xs shrink-0 text-primary"
+        aria-label="Workspace has active conversations"
+        title="A conversation in this workspace is generating"></span>
+    {/if}
+    <span>
+      {ws.conversationCount}
+      {ws.conversationCount === 1 ? "conversation" : "conversations"}
+    </span>
+    <span class="ml-auto font-mono opacity-70">{relativeTime(ws.lastActivityAt, Date.now())}</span>
+  </div>
+</div>