feat: full options UI for all new features + managed browser docs

Options UI additions:
- Auto Sync panel: enable/disable, method (Gist/URL), interval selector
- Version History: snapshot list with timestamps/source, restore buttons,
  max snapshots setting, clear history
- Connected Devices: device table with name/browser/last-sync, rename
  this device, remove other devices
- Organization: join by invite code or policy URL, compliance status,
  required mappings count, leave button (tamper-guarded)
- Tamper Protection: enable with admin password, change password,
  disable (requires admin password), org policy can prevent disabling
- Admin auth dialog: reusable <dialog> for any protected action
- Conflict Resolution: shows local vs remote values side-by-side with
  Keep Local / Keep Remote buttons

Service worker:
- Added autosync:config-changed and org:config-changed message handlers

README:
- Added managed browser deployment instructions for Chrome and Firefox

https://claude.ai/code/session_01SWSwDfMVij53bCTNSCLMwn

src/background/service-worker.js

@@ -159,6 +159,14 @@ const messageHandlers = {
     api.action.setBadgeBackgroundColor({ color: '#6b7280' });
   },
 
+  async 'autosync:config-changed'() {
+    await setupAutoSyncAlarm();
+  },
+
+  async 'org:config-changed'() {
+    await setupOrgPolicyAlarm();
+  },
+
   async 'get:locked-state'(_message, _sender, sendResponse) {
     const locked = await Storage.isLocked();
     sendResponse({ locked });