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/shared/state.ts

@@ -0,0 +1,62 @@
+/// Service-locator for cross-bundle state access.
+///
+/// Both popup.ts and vault.ts register themselves as the "host".
+/// All popup components import from here instead of from popup.ts,
+/// so the same component code works in either bundle.
+
+import type { Request, Response } from './messages';
+
+export interface StateHost {
+  getState(): any;
+  setState(partial: any): void;
+  navigate(view: string, extras?: any): void;
+  sendMessage(request: Request): Promise<Response>;
+  escapeHtml(s: string): string;
+  popOutToTab(): void;
+  isInTab(): boolean;
+  openVaultTab(hash?: string): void;
+}
+
+let host: StateHost | null = null;
+
+export function registerHost(h: StateHost): void { host = h; }
+
+export function getState(): any {
+  if (!host) throw new Error('No state host registered');
+  return host.getState();
+}
+
+export function setState(partial: any): void {
+  if (!host) throw new Error('No state host registered');
+  host.setState(partial);
+}
+
+export function navigate(view: string, extras?: any): void {
+  if (!host) throw new Error('No state host registered');
+  host.navigate(view, extras);
+}
+
+export function sendMessage(request: Request): Promise<Response> {
+  if (!host) throw new Error('No state host registered');
+  return host.sendMessage(request);
+}
+
+export function escapeHtml(s: string): string {
+  if (!host) throw new Error('No state host registered');
+  return host.escapeHtml(s);
+}
+
+export function popOutToTab(): void {
+  if (!host) throw new Error('No state host registered');
+  host.popOutToTab();
+}
+
+export function isInTab(): boolean {
+  if (!host) return false;
+  return host.isInTab();
+}
+
+export function openVaultTab(hash?: string): void {
+  if (!host) throw new Error('No state host registered');
+  host.openVaultTab(hash);
+}