feat(workspaces): sync the home tile layout per device orientation

The Win8-Start home grid's arrangement now syncs from the backend's
home-tile-layout plugin: ONE shared document per device orientation
(wide = landscape/desktop, tall = portrait/mobile) — every landscape
device renders the same layout, every portrait device the same other
one. localStorage persistence is retired (no migration — devices start
from the shared document; the first arrangement creates it).

- adapter/tile-layout-http.ts: the injected HTTP edge (GET/PUT/DELETE
  /home/tile-layout/:mode), the features/layout adapter's pattern
- tile-layout-store: server-backed, keyed by geometry mode — boot +
  orientation-change probes (stale in-flight responses never land),
  locally-applied edits + debounced full-document PUT with rollback to
  the last server document, WS push filtered to the active orientation,
  quiet ephemeral degrade when the backend is unreachable (no error UI),
  sync gated while a probe is in flight
- WorkspacesHome locks the store's orientation to the resolved grid
  geometry (the landscape/portrait split IS the device-type split)
- app store: the tile store lives beside the layout store; the WS
  dispatch feeds 'tile-layout' broadcasts into it; 'tiles' prop from
  App.svelte (the page entry owns the httpBase)
- ws adapter: the 'tile-layout' server message (parse guard) + socket
  handler; wire conformance case

1 files changed, 3 insertions, 2 deletions

diff --git a/src/features/workspaces/index.ts b/src/features/workspaces/index.ts
index a921617..1a60bb7 100644
--- a/src/features/workspaces/index.ts
+++ b/src/features/workspaces/index.ts
@@ -1,5 +1,6 @@
 export type { WorkspaceHttp, WorkspaceResult } from "./adapter/http";
 export { createWorkspaceHttp } from "./adapter/http";
+export { createTileLayoutHttp, type TileLayoutHttp } from "./adapter/tile-layout-http";
 export type {
   DragEmit,
   DragEvent as DragControllerEvent,
@@ -42,8 +43,8 @@ export {
 export { applyStarred, pageTitle, relativeTime, sortWorkspaces } from "./logic/view-model";
 export type { WorkspaceStore } from "./store.svelte";
 export { createWorkspaceStore } from "./store.svelte";
-export type { TileLayoutStore } from "./tile-layout-store.svelte";
-export { createTileLayoutStore, TILE_LAYOUT_STORAGE_KEY } from "./tile-layout-store.svelte";
+export type { TileLayoutProviderState, TileLayoutStore } from "./tile-layout-store.svelte";
+export { createTileLayoutStore } from "./tile-layout-store.svelte";
 export { default as WorkspacesHome } from "./ui/WorkspacesHome.svelte";
 
 /** Public module manifest — aggregated by the shell's "Loaded Modules" view. */