feat: strengthen module contracts and shared WebUI runtime

src/govoplan_core/server/fastapi.py

@@ -72,8 +72,19 @@ def _validate_production_startup() -> None:
         "off",
     }
     if throttle_enabled and not os.getenv("REDIS_URL", "").strip():
+        allow_process_local = os.getenv(
+            "GOVOPLAN_ALLOW_PROCESS_LOCAL_LOGIN_THROTTLE",
+            "false",
+        ).strip().lower() in {"1", "true", "yes", "on"}
+        if not allow_process_local:
+            raise RuntimeError(
+                "Production login throttling requires REDIS_URL. "
+                "Set GOVOPLAN_ALLOW_PROCESS_LOCAL_LOGIN_THROTTLE=true only "
+                "for an explicitly single-process deployment."
+            )
         logger.warning(
-            "Redis is not configured; login throttling is process-local and will not coordinate horizontally"
+            "Redis is not configured; login throttling is explicitly limited "
+            "to this process"
         )