feat(ext): shared state host — decouple components from popup.ts

Introduce shared/state.ts as a service-locator so popup components
(item-detail, item-form, trash, devices, settings, etc.) work in both
the popup and vault tab bundles. Both entry points register themselves
as the host; components import from shared/state instead of popup.ts.
Vault.ts now delegates to the real popup components, removing ~300 lines
of placeholder renderers.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

extension/src/popup/popup.ts

@@ -5,6 +5,7 @@
 
 import type { Request, Response } from '../shared/messages';
 import type { ItemId, ManifestEntry, Item } from '../shared/types';
+import { registerHost } from '../shared/state';
 import { renderUnlock } from './components/unlock';
 import { renderItemList } from './components/item-list';
 import { renderItemDetail } from './components/item-detail';
@@ -164,6 +165,19 @@ export function navigate(view: View, extras?: Partial<PopupState>): void {
   setState({ view, error: null, loading: false, ...extras });
 }
 
+// --- Register as state host so shared components can call back ---
+
+registerHost({
+  getState: () => currentState,
+  setState,
+  navigate,
+  sendMessage,
+  escapeHtml,
+  popOutToTab,
+  isInTab,
+  openVaultTab,
+});
+
 // --- Render ---
 
 function render(): void {