perf: Batch NIP-71 metadata fetches in NostrClient

Currently, when the NostrClient processes a burst of video events (e.g., initial
feed load), it triggers an individual NIP-71 metadata fetch for every video that
updates the `activeMap`. This results in a stampede of network requests (N videos
* M relays).

This change optimizes `flushEventBuffer` to collect all videos requiring metadata
updates and executes a single batched `populateNip71MetadataForVideos` call at
the end of the flush cycle.

This reduces the metadata fetch overhead from O(N) to O(1) per batch.

Verified with a local benchmark script (reduced fetch calls from 50 to 1 for 50 events)
and existing unit tests.

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

js/nostr/client.js

@@ -7650,6 +7650,7 @@ export class NostrClient {
 
       const toProcess = eventBuffer;
       eventBuffer = [];
+      const videosNeedingMetadata = [];
 
       for (const evt of toProcess) {
         try {
@@ -7706,23 +7707,30 @@ export class NostrClient {
             this.activeMap.set(activeKey, video);
             onVideo(video); // Trigger the callback that re-renders
 
-            // Fetch NIP-71 metadata (categorization tags) in the background
-            this.populateNip71MetadataForVideos([video])
-              .then(() => {
-                this.applyRootCreatedAt(video);
-              })
-              .catch((error) => {
-                devLogger.warn(
-                  "[nostr] Failed to hydrate NIP-71 metadata for live video:",
-                  error
-                );
-              });
+            // Defer NIP-71 fetch for batching
+            videosNeedingMetadata.push(video);
           }
         } catch (err) {
           devLogger.error("[subscribeVideos] Error processing event:", err);
         }
       }
 
+      if (videosNeedingMetadata.length > 0) {
+        // Fetch NIP-71 metadata (categorization tags) in the background
+        this.populateNip71MetadataForVideos(videosNeedingMetadata)
+          .then(() => {
+            for (const video of videosNeedingMetadata) {
+              this.applyRootCreatedAt(video);
+            }
+          })
+          .catch((error) => {
+            devLogger.warn(
+              "[nostr] Failed to hydrate NIP-71 metadata for live video batch:",
+              error,
+            );
+          });
+      }
+
       // Persist processed events after each flush so reloads warm quickly.
       this.saveLocalData("subscribeVideos:flush");
     };