Fix fresh-install pull skipping due to empty-profile timestamp pollution

Root cause: when the popup opens for the first time it calls
addProfile('Personal') + updateProfile(...) to create a default empty
profile. Both call saveProfiles, which was unconditionally setting
ss_lastModified: Date.now(). This made the new browser's local
timestamp look like right now — newer than any Gist data pushed by
the source browser — so every pull returned "Already up to date"
without ever prompting for a password or importing anything.

Fixes:

1. storage.js saveProfiles: only advance ss_lastModified when at
   least one profile contains real PII (non-empty real value in
   names, emails, usernames, phones, or catchAllEmail). Creating the
   default empty profile structure on first install leaves
   ss_lastModified at 0 so pulls correctly see remote data as newer.

2. sync.js pushToGist: persist ss_last_push_time and
   ss_last_push_source alongside ss_gist_id so the source browser
   (which only pushes) can also show its last activity time.

3. options.js: display both "Pushed: <time>" and "Pulled: <time>"
   in the Gist status area on page load, giving both browsers
   meaningful feedback.

4. service-worker.js: after a successful auto-sync pull, broadcast
   vault:unlocked to all open content-script tabs so substitution
   works immediately without a page reload.

https://claude.ai/code/session_01QJnEnLfbXKR5FSCQ3Qfs53

src/background/service-worker.js

@@ -472,6 +472,20 @@ api.alarms.onAlarm.addListener(async (alarm) => {
     const result = await SilentSendSync.performAutoSync();
     if (result.pulled) {
       console.log('[Silent Send] Auto-sync pulled new data');
+      // Broadcast decrypted data to all open content scripts so
+      // substitution works immediately without a page reload.
+      const mappings = await Storage.getMappings();
+      const identity = await Storage.getIdentity();
+      const settings = await Storage.getSettings();
+      const allPatterns = [...BUILTIN_URL_PATTERNS];
+      const customDomains = settings.customDomains || [];
+      for (const domain of customDomains) allPatterns.push(domain + '/*');
+      for (const urlPattern of allPatterns) {
+        const tabs = await api.tabs.query({ url: urlPattern }).catch(() => []);
+        for (const tab of tabs) {
+          api.tabs.sendMessage(tab.id, { type: 'vault:unlocked', mappings, identity, settings }).catch(() => {});
+        }
+      }
     }
     if (result.error) {
       console.warn('[Silent Send] Auto-sync error:', result.error);