feat: add "Retry All Errors" batch reanalyze button

Backend:
- POST /api/messages/reanalyze-batch — bulk reset error messages to pending
- messages.repository.reanalyzeErrorBatch() — scoped by guildId/channelId/messageIds
- messages.service.reanalyzeErrorBatch() — validation layer

Frontend:
- reanalyzeErrorBatch() API client function
- useMessages.reanalyzeAllErrors() — optimistic state + batch call
- MessagesPanel: destructive button visible when error count > 0
- Shows confirmation text with queued count

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/backend/src/modules/messages/messages.service.ts

@@ -45,6 +45,21 @@ export class MessagesService {
     logger.debug({ channelId, query }, "Getting attachments by channel");
     return messagesRepository.getAttachmentsByChannel(channelId, query);
   }
+
+  async reanalyzeErrorBatch(opts: {
+    guildId?: string;
+    channelId?: string;
+    messageIds?: string[];
+  }) {
+    if (!opts.guildId && !opts.channelId && (!opts.messageIds || opts.messageIds.length === 0)) {
+      throw new ValidationError(
+        "At least one of guildId, channelId, or messageIds[] is required",
+      );
+    }
+
+    logger.info(opts, "Batch reanalyzing errored messages");
+    return messagesRepository.reanalyzeErrorBatch(opts);
+  }
 }
 
 export const messagesService = new MessagesService();