Implement claim and freeze system for moderation queue

Refactors the moderation queue to implement a "claim and freeze" model, preventing automatic updates during background polling and enforcing claim/lock isolation. Adds a `claimSubmission` function to `useModerationQueue` and modifies `ModerationQueue.tsx` to filter submissions based on claim status and update handling.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: e14c2292-b0e5-43fe-b301-a4ad668949e9
Replit-Commit-Checkpoint-Type: intermediate_checkpoint

src/hooks/useModerationQueue.ts

@@ -305,6 +305,60 @@ export const useModerationQueue = () => {
     }
   }, [user, toast, fetchStats]);
 
+  // Claim a specific submission (CRM-style claim any)
+  const claimSubmission = useCallback(async (submissionId: string): Promise<boolean> => {
+    if (!user?.id) {
+      toast({
+        title: 'Authentication Required',
+        description: 'You must be logged in to claim submissions',
+        variant: 'destructive',
+      });
+      return false;
+    }
+
+    setIsLoading(true);
+    try {
+      const expiresAt = new Date(Date.now() + 15 * 60 * 1000);
+      
+      const { error } = await supabase
+        .from('content_submissions')
+        .update({
+          assigned_to: user.id,
+          assigned_at: new Date().toISOString(),
+          locked_until: expiresAt.toISOString(),
+        })
+        .eq('id', submissionId)
+        .or(`assigned_to.is.null,locked_until.lt.${new Date().toISOString()}`); // Only if unclaimed or lock expired
+
+      if (error) throw error;
+
+      setCurrentLock({
+        submissionId,
+        expiresAt,
+      });
+
+      startLockTimer(expiresAt);
+      fetchStats();
+
+      toast({
+        title: 'Submission Claimed',
+        description: 'You now have 15 minutes to review this submission',
+      });
+
+      return true;
+    } catch (error: any) {
+      console.error('Error claiming submission:', error);
+      toast({
+        title: 'Error',
+        description: error.message || 'Failed to claim submission',
+        variant: 'destructive',
+      });
+      return false;
+    } finally {
+      setIsLoading(false);
+    }
+  }, [user, toast, startLockTimer, fetchStats]);
+
   // Reassign submission
   const reassignSubmission = useCallback(async (submissionId: string, newModeratorId: string): Promise<boolean> => {
     if (!user?.id) return false;
@@ -355,6 +409,7 @@ export const useModerationQueue = () => {
     queueStats,
     isLoading,
     claimNext,
+    claimSubmission,
     extendLock,
     releaseLock,
     getTimeRemaining,