chore: sync annotation UI, shortcuts, and misc updates

frontend/src/app.css

@@ -710,7 +710,7 @@ main.page {
 
 .shortcuts { margin: 0; display: grid; gap: 5px; font-size: 12px; }
 .shortcuts > div { display: flex; gap: 10px; align-items: baseline; }
-.shortcuts dt { flex: none; width: 62px; }
+.shortcuts dt { flex: none; width: 72px; }
 .shortcuts dd { margin: 0; color: var(--text-muted); }
 
 kbd {

frontend/src/components/AnnotationCanvas.jsx

@@ -75,6 +75,17 @@ export default function AnnotationCanvas({
 
   const additive = useRef(false)
 
+  function handleDoubleClick(event) {
+    if (selecting) return
+    const [x, y] = pointAt(event)
+    if (assistMode) {
+      const seed = [Math.max(0, x - 0.015), Math.max(0, y - 0.015), Math.min(1, x + 0.015), Math.min(1, y + 0.015)]
+      onAssist(seed)
+    } else if (onExemplar) {
+      onExemplar([x, y], !event.shiftKey, { kind: 'point' })
+    }
+  }
+
   function startDraw(event) {
     if (event.button !== 0) return
     const [x, y] = pointAt(event)
@@ -218,6 +229,7 @@ export default function AnnotationCanvas({
         onPointerDown={startDraw}
         onPointerMove={onPointerMove}
         onPointerUp={onPointerUp}
+        onDoubleClick={handleDoubleClick}
       >
         {/* A preview replaces this class on the frame wholesale, so its stored
             shapes step aside for the proposals — left on screen they read as
@@ -270,7 +282,7 @@ export default function AnnotationCanvas({
           )
         })}
 
-        {!selecting && exemplars.map((item, i) => {
+        {!selecting && exemplars.filter((item) => item.kind !== 'point' && item.box).map((item, i) => {
           const [x0, y0, x1, y1] = item.box
           return (
             <rect

frontend/src/components/ShortcutsPanel.jsx

@@ -7,6 +7,10 @@ export default function ShortcutsPanel() {
           <dt><kbd>Drag</kbd></dt>
           <dd>Example of this class → preview a re-detect</dd>
         </div>
+        <div>
+          <dt><kbd>Dbl Click</kbd></dt>
+          <dd>Quick exemplar point → preview a re-detect</dd>
+        </div>
         <div>
           <dt><kbd>Enter</kbd> <kbd>Esc</kbd></dt>
           <dd>Apply / discard the preview</dd>
@@ -15,6 +19,10 @@ export default function ShortcutsPanel() {
           <dt><kbd>Shift</kbd>+<kbd>Drag</kbd></dt>
           <dd>Not this → drop it and re-detect</dd>
         </div>
+        <div>
+          <dt><kbd>Shift</kbd>+<kbd>Dbl</kbd></dt>
+          <dd>Quick negative exemplar point</dd>
+        </div>
         <div>
           <dt><kbd>V</kbd></dt>
           <dd>Draw ⇄ Select mode</dd>

frontend/src/hooks/useExemplarPool.js

@@ -100,9 +100,12 @@ export default function useExemplarPool({ frameId, classId, onApplied, onError,
     timer.current = setTimeout(() => runRef.current?.(), delay)
   }, [])
 
-  const add = useCallback((box, positive) => {
+  const add = useCallback((target, positive, { kind = 'box' } = {}) => {
     if (!frameId) return
-    poolRef.current = [...poolRef.current, { box, positive }]
+    const entry = kind === 'point'
+      ? { point: target, positive, kind: 'point' }
+      : { box: target, positive, kind: 'box' }
+    poolRef.current = [...poolRef.current, entry]
     setExemplars(poolRef.current)
     setActive(true)
     // A drag during a pass cannot be in that pass's result, so it always earns

frontend/src/pages/ReviewPage.jsx

@@ -500,7 +500,7 @@ export default function ReviewPage({ batchId: rawBatchId, projectId, onProject }
                   ? `${pool.exemplars.filter((e) => e.positive).length} example(s), `
                     + `${pool.exemplars.filter((e) => !e.positive).length} negative — `
                     + 'tune the filters, then Apply'
-                  : 'Drag an example of this class · Shift-drag = not this'}
+                  : 'Drag or double-click an example · Shift-drag/click = not this'}
               </span>
             )}
           </div>