feat(review): GT-aware TP/FP/FN frame annotation + scene-detector examples

dump_error_frames.py drew every identified box green, so a false positive looked
like a true positive and a missed cast member was invisible. Make the annotation
ground-truth aware, matching what the per-second scorer classifies:
  - GREEN  true positive  — a name X-Ray also credits to this scene
  - RED    false positive — a name X-Ray does NOT credit here (the real error)
  - ORANGE unknown detection
  - BLUE   a text panel listing X-Ray cast present with no detected face (the
           structural false-negatives — no box exists to draw)

Add two representative annotated frames to the scene-detector page: a clean
green-TP second, and the face-vs-scene-cast case (a red FP lead + six off-camera
cast in blue) that makes the recall ceiling visual. Frames are generated by the
script from replay.py --raw-out output; the two committed examples are hand-picked
doc assets (bulk experiments/dump_review is regenerable and gitignored).

scripts/optimizer/dump_error_frames.py

@@ -121,23 +121,44 @@ def load_raw_annotations(raw_path: str):
     return by_second
 
 
-def draw_annotations(frame_path: Path, actors: list):
+def _name_key(name: str) -> str:
+    """Normalised match key, mirroring identity.py's name: fallback."""
+    return "name:" + "".join(ch for ch in name.lower() if ch.isalnum() or ch == " ").strip()
+
+
+def draw_annotations(frame_path: Path, actors: list, fp_keys=None, fn_names=None):
+    """Draw GT-aware boxes: GREEN = true positive (named actor X-Ray also has in
+    this scene), RED = false positive (named actor NOT in the scene → the real
+    error), ORANGE = unknown detection. FN cast (present per X-Ray but no face
+    detected — so no box to draw) is listed as a BLUE text panel bottom-left."""
     img = cv2.imread(str(frame_path))
     if img is None:
         return
+    fp_keys = fp_keys or set()
+    GREEN, RED, ORANGE, BLUE = (60,200,0), (0,0,230), (220,100,0), (230,150,0)
     for a in actors:
         known = a.get("actor_idx", -1) >= 0
-        colour = (60, 200, 0) if known else (220, 100, 0)  # BGR: green / orange
-        x, y, w, h = a["bbox"]
-        x, y, w, h = int(x), int(y), int(w), int(h)
+        if known:
+            colour = RED if _name_key(a["name"]) in fp_keys else GREEN
+            label = f"{a['name']} {a['similarity']*100:.0f}%"
+        else:
+            colour = ORANGE; label = f"unknown {a['similarity']*100:.0f}%"
+        x, y, w, h = (int(v) for v in a["bbox"])
         cv2.rectangle(img, (x, y), (x + w, y + h), colour, 2)
-
-        label = f"{a['name']} {a['similarity']*100:.0f}%" if known else f"unknown {a['similarity']*100:.0f}%"
-        (tw, th), baseline = cv2.getTextSize(label, cv2.FONT_HERSHEY_SIMPLEX, 0.5, 1)
-        strip_y0 = max(0, y - th - 4)
-        cv2.rectangle(img, (x, strip_y0), (x + tw + 4, y), colour, cv2.FILLED)
-        cv2.putText(img, label, (x + 2, y - 2), cv2.FONT_HERSHEY_SIMPLEX, 0.5,
-                    (255, 255, 255), 1, cv2.LINE_AA)
+        (tw, th), _ = cv2.getTextSize(label, cv2.FONT_HERSHEY_SIMPLEX, 0.5, 1)
+        cv2.rectangle(img, (x, max(0, y-th-4)), (x+tw+4, y), colour, cv2.FILLED)
+        cv2.putText(img, label, (x+2, y-2), cv2.FONT_HERSHEY_SIMPLEX, 0.5,
+                    (255,255,255), 1, cv2.LINE_AA)
+    # FN: X-Ray cast present with no detected face — no box exists, so list them.
+    fn = [n for n in (fn_names or []) if n]
+    if fn:
+        H = img.shape[0]
+        cv2.putText(img, "off-screen / missed (X-Ray cast, no face):",
+                    (8, H-8-18*len(fn[:6])), cv2.FONT_HERSHEY_SIMPLEX, 0.45, BLUE, 1, cv2.LINE_AA)
+        for i, n in enumerate(fn[:6]):
+            disp = n.replace("name:", "").title()
+            cv2.putText(img, f"  {disp}", (8, H-8-18*(len(fn[:6])-1-i)),
+                        cv2.FONT_HERSHEY_SIMPLEX, 0.5, BLUE, 1, cv2.LINE_AA)
     cv2.imwrite(str(frame_path), img)
 
 
@@ -183,7 +204,9 @@ def main():
                 extract_frame(args.movie, r["t"], out_path)
                 ok = True
                 if raw_by_second is not None:
-                    draw_annotations(out_path, raw_by_second.get(r["t"], []))
+                    fp_keys = {_name_key(n) for n in r["fp"]}
+                    draw_annotations(out_path, raw_by_second.get(r["t"], []),
+                                     fp_keys=fp_keys, fn_names=r["fn"])
             except subprocess.CalledProcessError as e:
                 ok = False
                 print(f"[dump_error_frames] ffmpeg failed at t={r['t']}: {e}", file=sys.stderr)