feat: add /api/version endpoint with IMAGE_TAG; validate in ci healthcheck

backend/app/__init__.py

@@ -53,6 +53,7 @@ def create_app(config_name: str | None = None) -> Flask:
     from app.routes.analytics import analytics_bp, _should_track, record_page_view
     from app.routes.config import config_bp
     from app.routes.agents import agents_public_bp, agents_admin_bp
+    from app.routes.version import version_bp
 
     app.register_blueprint(homepage_bp)
     app.register_blueprint(properties_bp)
@@ -65,6 +66,7 @@ def create_app(config_name: str | None = None) -> Flask:
     app.register_blueprint(config_bp)
     app.register_blueprint(agents_public_bp)
     app.register_blueprint(agents_admin_bp)
+    app.register_blueprint(version_bp)
 
     @app.route("/health")
     def health():