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/state/profileCache.js

@@ -168,6 +168,7 @@ class ProfileCache {
     // But if services manage runtime state, `profileCache` acts as the persistence layer.
 
     this.emit("update", { pubkey, section, data });
+    this.emit("partition-updated", { pubkey, key: section });
   }
 
   // Runtime memory cache methods (for decrypted data, if services want to use it)
@@ -197,6 +198,15 @@ class ProfileCache {
     }
   }
 
+  clearSignerRuntime(pubkey) {
+    const normalized = this.normalizeHexPubkey(pubkey);
+    if (!normalized) {
+      return;
+    }
+    this.clearMemoryCache(normalized);
+    this.emit("runtimeCleared", { pubkey: normalized });
+  }
+
   subscribe(callback) {
     this.listeners.add(callback);
     return () => this.listeners.delete(callback);