feat(provenance): /api/provenance image + post endpoints

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/api/__init__.py

@@ -20,6 +20,7 @@ def all_blueprints() -> list[Blueprint]:
     from .gallery import gallery_bp
     from .import_admin import import_admin_bp
     from .ml_admin import ml_admin_bp
+    from .provenance import provenance_bp
     from .settings import settings_bp
     from .showcase import showcase_bp
     from .suggestions import suggestions_bp
@@ -27,6 +28,7 @@ def all_blueprints() -> list[Blueprint]:
     return [
         api_bp,
         gallery_bp,
+        provenance_bp,
         tags_bp,
         artist_bp,
         showcase_bp,