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/frontend/src/features/messages/hooks/useMessages.ts

@@ -1,6 +1,6 @@
 import { useCallback, useRef, useState } from "react";
 import type { MessageRecord } from "../../../shared/api/client";
-import { listMessages, reanalyzeMessage } from "../../../shared/api/client";
+import { listMessages, reanalyzeErrorBatch, reanalyzeMessage } from "../../../shared/api/client";
 
 const PAGE_SIZE = 100;
 
@@ -91,6 +91,29 @@ export function useMessages() {
     await reanalyzeMessage(id);
   }, []);
 
+  const reanalyzeAllErrors = useCallback(
+    async (): Promise<number> => {
+      // Optimistically mark all error messages as pending
+      setMessages((prev) =>
+        prev.map((message) =>
+          message.ai_status === "error"
+            ? {
+                ...message,
+                ai_status: "pending" as const,
+                ai_error: null,
+                ai_analysis: null,
+              }
+            : message,
+        ),
+      );
+      const { count } = await reanalyzeErrorBatch({
+        guildId: currentGuild.current ?? undefined,
+      });
+      return count;
+    },
+    [],
+  );
+
   return {
     messages,
     setMessages,
@@ -99,6 +122,7 @@ export function useMessages() {
     error,
     fetchMessages,
     reanalyze,
+    reanalyzeAllErrors,
     loadMore,
     hasMore,
   };