fc5: lift Quart request body cap to 1 GiB so large IR exports don't 413

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

backend/app/__init__.py

@@ -23,6 +23,12 @@ def create_app() -> Quart:
 
     app = Quart(__name__)
     app.secret_key = cfg.secret_key
+    # FC-5: legacy IR ingest JSON can run to tens of MB (hundreds of
+    # thousands of image_tag_associations). Werkzeug's default form
+    # memory cap is 500KB; raise both ceilings so the multipart upload
+    # for /api/migrate/ir_ingest doesn't 413.
+    app.config["MAX_CONTENT_LENGTH"] = 1024 * 1024 * 1024   # 1 GB
+    app.config["MAX_FORM_MEMORY_SIZE"] = 1024 * 1024 * 1024  # 1 GB
 
     for bp in all_blueprints():
         app.register_blueprint(bp)