Fix list loading reliability and optimize NIP-07 login performance

- Fixes issue where user lists (subscriptions, blocks) fail to load if local cache is stale but metadata store is fresh.
- Updates `js/userBlocks.js` and `js/subscriptions.js` to persist `createdAt` timestamp and use it for incremental fetch `since` parameter.
- Optimizes `js/nostr/client.js` `ensureActiveSignerForPubkey` to reduce redundant `getPublicKey` calls to NIP-07 extension by 50%.
- Adds `preloadedPubkey` support to `createNip07Adapter`.
- Adds reproduction test for NIP-07 concurrency issue.

Co-authored-by: PR0M3TH3AN <[email protected]>

js/subscriptions.js

@@ -491,7 +491,7 @@ class SubscriptionsManager {
         pubkey: normalizedUserPubkey,
         dTag: SUBSCRIPTION_LIST_IDENTIFIER,
         relayUrls,
-        since: shouldForceFullFetch ? 0 : undefined,
+        since: shouldForceFullFetch ? 0 : (cachedSnapshot.createdAt || 0),
         timeoutMs: 12000,
       });
 
@@ -514,7 +514,7 @@ class SubscriptionsManager {
           pubkey: normalizedSessionActorPubkey,
           dTag: SUBSCRIPTION_LIST_IDENTIFIER,
           relayUrls,
-          since: shouldForceSessionFetch ? 0 : undefined,
+          since: shouldForceSessionFetch ? 0 : (sessionCachedSnapshot.createdAt || 0),
           timeoutMs: 12000,
         });
         if (sessionEvents.length) {