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, 171 insertions, 0 deletions

diff --git a/src/features/workspaces/ui/HomeHeader.svelte b/src/features/workspaces/ui/HomeHeader.svelte
new file mode 100644
index 0000000..01ac63f
--- /dev/null
+++ b/src/features/workspaces/ui/HomeHeader.svelte
@@ -0,0 +1,171 @@
+<script lang="ts">
+  import { isValidSlug } from "../logic/route";
+
+  /** The create outcome the page reports back to the popover. */
+  export type CreateResult = { readonly ok: true } | { readonly ok: false; readonly error: string };
+
+  let {
+    compact = false,
+    withPlugins = false,
+    withSort = false,
+    onCreate,
+    onOpenPlugins,
+    onSort,
+  }: {
+    /** Tall geometry: the controls collapse to compact icon buttons and the
+     * new-workspace popover becomes a bottom sheet. */
+    compact?: boolean;
+    /** The plugins port is present → the Plugins button renders. */
+    withPlugins?: boolean;
+    /** The Sort overflow action renders (recent-activity re-apply). */
+    withSort?: boolean;
+    /** Create the workspace on the backend (does NOT navigate); the page
+     * places the new tile + enters rename mode. */
+    onCreate: (slug: string) => Promise<CreateResult>;
+    onOpenPlugins: () => void;
+    onSort: () => void;
+  } = $props();
+
+  // ── New workspace popover (today's inline form logic, preserved) ──────────
+  let newSlug = $state("");
+  let slugError = $state<string | null>(null);
+  let popoverOpen = $state(false);
+  let submitting = $state(false);
+  let slugInput = $state<HTMLInputElement | undefined>();
+
+  const slugValid = $derived(newSlug.length > 0 && isValidSlug(newSlug));
+
+  function openPopover(): void {
+    popoverOpen = true;
+    slugError = null;
+    queueMicrotask(() => slugInput?.focus());
+  }
+
+  function closePopover(): void {
+    popoverOpen = false;
+    newSlug = "";
+    slugError = null;
+  }
+
+  async function submit(): Promise<void> {
+    const slug = newSlug.trim();
+    if (!isValidSlug(slug)) {
+      slugError = "Lowercase letters, digits, and hyphens (1–40 chars).";
+      return;
+    }
+    slugError = null;
+    submitting = true;
+    const result = await onCreate(slug);
+    submitting = false;
+    if (!result.ok) {
+      slugError = result.error;
+      return;
+    }
+    closePopover();
+  }
+</script>
+
+<header class="flex shrink-0 items-center justify-between gap-2 px-6 py-4">
+  <h1 class="text-3xl font-black tracking-tight">Dispatch</h1>
+
+  <div class="flex items-center gap-2" class:gap-1={compact}>
+    <!-- New workspace -->
+    <button
+      type="button"
+      class="btn btn-primary btn-sm"
+      class:btn-circle={compact}
+      aria-label="New workspace"
+      title="New workspace"
+      onclick={() => (popoverOpen ? closePopover() : openPopover())}
+    >
+      {#if compact}
+        <span aria-hidden="true" class="text-lg leading-none">+</span>
+      {:else}
+        New workspace
+      {/if}
+    </button>
+
+    {#if withPlugins}
+      <button
+        type="button"
+        class="btn btn-outline btn-sm"
+        class:btn-circle={compact}
+        aria-label="Plugins"
+        title="Open the plugin manager (load/unload plugins globally)"
+        onclick={onOpenPlugins}
+      >
+        {#if compact}
+          <span aria-hidden="true">⚡</span>
+        {:else}
+          Plugins
+        {/if}
+      </button>
+    {/if}
+
+    {#if withSort}
+      <div class="dropdown dropdown-end">
+        <button type="button" class="btn btn-ghost btn-sm" aria-label="More actions" title="More">
+          ⋯
+        </button>
+        <ul class="dropdown-content menu z-50 w-52 rounded-box border border-base-content/15 bg-base-100 p-2 shadow-xl">
+          <li>
+            <button type="button" onclick={onSort}>Sort by recent activity</button>
+          </li>
+        </ul>
+      </div>
+    {/if}
+  </div>
+</header>
+
+{#if popoverOpen}
+  <!-- Backdrop closes the popover. -->
+  <button
+    type="button"
+    class="fixed inset-0 z-40 cursor-default"
+    aria-label="Close new workspace"
+    onclick={closePopover}></button>
+
+  <!-- One popover body; the geometry only changes its positioning (bottom
+       sheet on tall screens, a corner card on wide ones). -->
+  <div
+    class="fixed z-50 border border-base-content/15 bg-base-100 p-4 shadow-2xl"
+    class:inset-x-0={compact}
+    class:bottom-0={compact}
+    class:rounded-t-box={compact}
+    class:top-14={!compact}
+    class:right-6={!compact}
+    class:w-80={!compact}
+    class:rounded-box={!compact}
+  >
+    <form
+      class="flex flex-col gap-2"
+      onsubmit={(e) => {
+        e.preventDefault();
+        void submit();
+      }}
+    >
+      <label for="new-ws" class="text-xs font-semibold uppercase opacity-60">New workspace</label>
+      <input
+        id="new-ws"
+        bind:this={slugInput}
+        class="input input-bordered w-full"
+        placeholder="my-workspace"
+        bind:value={newSlug}
+        autocomplete="off"
+        spellcheck="false"
+      />
+      {#if slugError}<p class="text-xs text-error">{slugError}</p>{/if}
+      <div class="flex justify-end gap-2">
+        {#if compact}
+          <button type="button" class="btn btn-ghost btn-sm" onclick={closePopover}>Cancel</button>
+        {/if}
+        <button type="submit" class="btn btn-primary btn-sm" disabled={!slugValid || submitting}>
+          {#if submitting}
+            <span class="loading loading-spinner loading-xs"></span>
+          {/if}
+          Create
+        </button>
+      </div>
+    </form>
+  </div>
+{/if}