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/components/__tests__/settings-vault.test.ts

@@ -1,6 +1,6 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 
-vi.mock('../../popup', async () => {
+vi.mock('../../../shared/state', async () => {
   const navigate = vi.fn();
   const setState = vi.fn();
   const sendMessage = vi.fn();
@@ -25,7 +25,7 @@ vi.mock('../../popup', async () => {
   const escapeHtml = (s: string) => s
     .replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;')
     .replace(/"/g, '&quot;').replace(/'/g, '&#39;');
-  return { navigate, setState, sendMessage, getState, escapeHtml };
+  return { navigate, setState, sendMessage, getState, escapeHtml, popOutToTab: vi.fn(), isInTab: vi.fn(() => false), openVaultTab: vi.fn() };
 });
 
 vi.mock('../generator-panel', () => ({
@@ -34,7 +34,7 @@ vi.mock('../generator-panel', () => ({
 }));
 
 import { renderVaultSettings } from '../settings-vault';
-import { sendMessage } from '../../popup';
+import { sendMessage } from '../../../shared/state';
 
 describe('settings-vault', () => {
   beforeEach(() => {