refactor: 移除 Python upstream 依赖，清理全部 legacy/Python 兼容层

- 移除 upstream_base_url 参数及 AETHER_GATEWAY_UPSTREAM 环境变量，gateway 不再需要指向 Python 宿主
- 删除所有 LEGACY_*/PYTHON_* 常量、路由组、header 定义及 sunset/phaseout 机制
- 将 legacy_gateway_bridge 重命名为 internal_gateway，executor 相关命名统一为 execution_runtime
- dev.sh 新增 Postgres/Redis 预检查，移除 upstream 相关启动参数和提示
- 新增 ai_public 路由处理器
- 全量适配 handler、test、state、control 等模块的命名和接口变更

apps/aether-gateway/src/maintenance/runtime/runners.rs

@@ -1,4 +1,15 @@
-use super::*;
+use tracing::info;
+
+use crate::gateway::gateway_data::GatewayDataState;
+use crate::gateway::{AppState, GatewayError};
+
+use super::{
+    cleanup_audit_logs_once, cleanup_expired_gemini_file_mappings_once,
+    cleanup_request_candidates_once, cleanup_stale_pending_requests_once,
+    perform_db_maintenance_once, perform_provider_checkin_once, perform_stats_aggregation_once,
+    perform_stats_hourly_aggregation_once, perform_usage_cleanup_once,
+    perform_wallet_daily_usage_aggregation_once, summarize_postgres_pool,
+};
 
 pub(super) async fn run_audit_cleanup_once(
     data: &GatewayDataState,