feat: sequential task IDs (HQ-1, HQ-2, etc.)

- Add serial task_number column to tasks table
- Display HQ-{number} on cards and detail panel
- API resolveTask() supports UUID, number, or HQ-N prefix
- GET /api/tasks/:id endpoint for single task lookup
- All PATCH/POST/DELETE endpoints resolve by number or UUID

frontend/src/components/TaskCard.tsx

@@ -66,18 +66,9 @@ export function TaskCard({
   isActive,
   onClick,
 }: TaskCardProps) {
-  const [idCopied, setIdCopied] = useState(false);
   const actions = statusActions[task.status] || [];
   const noteCount = task.progressNotes?.length || 0;
-  const shortId = task.id.slice(0, 8);
-
-  const handleCopyId = (e: React.MouseEvent) => {
-    e.stopPropagation();
-    navigator.clipboard.writeText(task.id).then(() => {
-      setIdCopied(true);
-      setTimeout(() => setIdCopied(false), 1500);
-    });
-  };
+  const displayId = task.taskNumber ? `HQ-${task.taskNumber}` : task.id.slice(0, 8);
 
   return (
     <div
@@ -104,14 +95,14 @@ export function TaskCard({
 
           <div className="flex items-center gap-2 mb-2 flex-wrap">
             <span
-              className="text-xs px-1.5 py-0.5 rounded font-mono bg-gray-100 text-gray-500 cursor-pointer hover:bg-gray-200 transition"
-              title={`Click to copy: ${task.id}`}
+              className="text-xs px-1.5 py-0.5 rounded font-mono font-bold bg-amber-100 text-amber-700 cursor-pointer hover:bg-amber-200 transition"
+              title={`Click to copy: ${displayId}`}
               onClick={(e) => {
                 e.stopPropagation();
-                navigator.clipboard.writeText(task.id);
+                navigator.clipboard.writeText(displayId);
               }}
             >
-              {task.id.slice(0, 8)}
+              {displayId}
             </span>
             <span className={`text-xs px-2 py-0.5 rounded-full font-medium ${priorityColors[task.priority]}`}>
               {task.priority}
@@ -127,17 +118,6 @@ export function TaskCard({
                 💬 {noteCount}
               </span>
             )}
-            <button
-              onClick={handleCopyId}
-              className="text-xs font-mono text-gray-300 hover:text-amber-600 transition cursor-pointer ml-auto"
-              title={`Copy full ID: ${task.id}`}
-            >
-              {idCopied ? (
-                <span className="text-green-500">✓ copied</span>
-              ) : (
-                <span>{shortId}…</span>
-              )}
-            </button>
           </div>
 
           {task.description && (