Implement profile-scoped caching and signer invalidation logic

- Updated `profileCache.js` to support clearing runtime memory on signer change.
- Updated `NostrClient` to trigger `clearSignerRuntime` on `setActiveSigner`.
- Updated list services (`subscriptions`, `userBlocks`, `hashtagPreferences`, `watchHistory`) to listen for `runtimeCleared` and reload data.
- Updated `NostrClient` sync metadata methods to default to the active profile pubkey.
- Added `partition-updated` event emission to `profileCache`.

js/subscriptions.js

@@ -246,6 +246,11 @@ class SubscriptionsManager {
         this.reset();
         // Optionally reload immediately if we have a pubkey?
         // Usually UI triggers reload via showSubscriptionVideos
+      } else if (event === "runtimeCleared" && detail.pubkey === this.currentUserPubkey) {
+        this.reset();
+        if (this.currentUserPubkey) {
+          this.loadSubscriptions(this.currentUserPubkey);
+        }
       }
     });
   }