fix(vwb): import lit anchor_image_base64 dans target.context_hints

Le converter convert_learned_to_vwb_steps ne lisait l'ancre que dans
target/screenshot/action.parameters, jamais dans target.context_hints
où le recorder la range réellement -> anchor_id NULL a l'import.
Ajout de la source context_hints (fallback or, additif, non regressif).
Preuve: import reel 'Explorateur — session' -> 4/5 steps anchor_id non NULL
+ 4 PNG, x_pct/y_pct preserves.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

visual_workflow_builder/backend/services/learned_workflow_bridge.py

@@ -226,6 +226,7 @@ def convert_learned_to_vwb_steps(
             anchor_b64 = (
                 target.get("anchor_image_base64")
                 or target.get("screenshot")
+                or (target.get("context_hints") or {}).get("anchor_image_base64")
                 or action_params.get("anchor_image_base64")
             )
             if anchor_b64: