Fix pull silently skipping on fresh browser install; show last pull time

Three issues in the Gist pull flow on a browser with no prior data:

1. _getAllData() returned Date.now() as lastModified when ss_lastModified
   was unset (fresh install). The timestamp check in pullFromGist then
   saw the Gist data as older than local, silently returned imported:false
   ("Already up to date") without importing anything or prompting for
   auth. Fixed by using || 0 so a browser with no data always accepts
   remote data as newer.

2. _applyData now persists ss_last_pull_time and ss_last_pull_source so
   the last successful pull survives page reloads.

3. The Gist section on the options page now shows "Last pulled: <time>"
   alongside the Gist ID on load, so both browsers display their sync
   status rather than showing nothing on first open.

https://claude.ai/code/session_01QJnEnLfbXKR5FSCQ3Qfs53

src/lib/sync.js

@@ -901,7 +901,7 @@ const SilentSendSync = {
     const result = await api.storage.local.get('ss_lastModified');
     return {
       version: '1',
-      lastModified: result.ss_lastModified || Date.now(),
+      lastModified: result.ss_lastModified || 0,
       identity: identity || {},
       mappings: mappings || [],
       settings: settings || {},
@@ -924,9 +924,12 @@ const SilentSendSync = {
     }
 
     // Metadata stays plaintext
+    const now = Date.now();
     await api.storage.local.set({
       ss_lastModified: data.lastModified,
-      ss_sync_notification: { source, time: Date.now() },
+      ss_sync_notification: { source, time: now },
+      ss_last_pull_time: now,
+      ss_last_pull_source: source,
     });
   },