refactor: nettoyage agent + fix SomEngine review (singleton partagé, cache, thread-safe)

Nettoyage Windows agent :
- Suppression lea_ui inutilisés (chat_widget, overlay, styles, etc. — -1991 lignes)
- Suppression window_info*.py dupliqués (racine + core/ — -494 lignes)
- build/ + dist/ supprimés (48 MB PyInstaller abandonné, gitignorés)

Fix SomEngine (review quality guardian) :
- Singleton GPU partagé via get_shared_engine() (1 instance au lieu de 2)
- Thread-safe avec threading.Lock (double-checked locking)
- Cache SomResult par screenshot_id (max 50, évite YOLO+OCR redondants)
- Fuite fichier temp docTR corrigée (finally block)
- Chemin YOLO configurable via SOM_YOLO_WEIGHTS env var
- Guard som_image None avant VLM
- Match texte partiel : len(label) >= 3

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

agent_v0/server_v1/api_stream.py

@@ -3326,21 +3326,13 @@ def _vlm_quick_find(
 # Résolution Set-of-Mark : SomEngine (détection) + VLM (identification)
 # ---------------------------------------------------------------------------
 
-_som_engine_api = None  # Singleton
-
-
 def _get_som_engine_api():
-    """Singleton SomEngine pour la résolution visuelle (lazy-loaded, GPU)."""
-    global _som_engine_api
-    if _som_engine_api is None:
-        try:
-            from core.detection.som_engine import SomEngine
-            _som_engine_api = SomEngine(device="cuda")
-            logger.info("SomEngine API initialisé (lazy singleton)")
-        except Exception as e:
-            logger.warning("SomEngine API non disponible : %s", e)
-            _som_engine_api = False
-    return _som_engine_api if _som_engine_api is not False else None
+    """Singleton SomEngine partagé."""
+    try:
+        from core.detection.som_engine import get_shared_engine
+        return get_shared_engine()
+    except ImportError:
+        return None
 
 
 def _resolve_by_som(
@@ -3423,7 +3415,7 @@ def _resolve_by_som(
         if not exact_matches:
             exact_matches = [
                 e for e in som_result.elements
-                if e.label and (
+                if e.label and len(e.label) >= 3 and (
                     label_lower in e.label.lower()
                     or e.label.lower() in label_lower
                 )
@@ -3493,6 +3485,10 @@ def _resolve_by_som(
             )
 
     # ── 3. Sauvegarder l'image annotée SoM temporairement ──
+    if som_result.som_image is None:
+        logger.debug("SoM resolve : pas d'image annotée, skip VLM")
+        return None
+
     import tempfile
     try:
         with tempfile.NamedTemporaryFile(suffix=".jpg", delete=False) as tmp: