feat(views,surface-host): Extensions sidebar view — auto-expanded surfaces + tables

views (new feature):
- pure panel-stack reducer + thin generic ViewSidebar (dropdown picker + add/remove),
  switches on view KIND, never a surface id

Extensions view (composition root):
- folds frontend modules + backend surfaces into one "Extensions" view
- frontend module list AGGREGATED from each feature's public `manifest` export
  (can't drift); no per-module version (FE features are internal to dispatch-web)
- surfaces are AUTO-SUBSCRIBED on catalog + rendered expanded (no catalog buttons)

surface-host:
- consecutive `stat` fields coalesce into one aligned label/value table (StatTable)
- generic custom-field renderer: dispatch on rendererId === "table" → SurfaceTable
  (pure parseTablePayload), so a backend `custom`/table field renders generically
- shared presentational components/Table.svelte (used by both, neither feature
  depends on the other)

store:
- auto-subscribe every catalog entry, unsubscribe vanished ones, re-subscribe all
  on reconnect; expose all received specs via `surfaces` (drops single-selection)

backend-handoff: CR-1 — emit Loaded Extensions as a custom/table field; notes
what's already covered FE-side (renderer shipped, stat-table fallback works).

1 files changed, 6 insertions, 0 deletions

diff --git a/src/features/chat/index.ts b/src/features/chat/index.ts
index ae3e1f8..18ed693 100644
--- a/src/features/chat/index.ts
+++ b/src/features/chat/index.ts
@@ -7,3 +7,9 @@ export { createChatStore } from "./store.svelte";
 export { default as ChatView } from "./ui/ChatView.svelte";
 export { default as Composer } from "./ui/Composer.svelte";
 export { default as ModelSelector } from "./ui/ModelSelector.svelte";
+
+/** Public module manifest — aggregated by the shell's "Loaded Modules" view. */
+export const manifest = {
+	name: "chat",
+	description: "Conversation turns, composer, model selector, and metrics",
+} as const;