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/rate_limit.rs

@@ -529,7 +529,7 @@ mod tests {
             local_rejection: None,
             allowed_models: None,
         });
-        let state = AppState::new("http://127.0.0.1:1").expect("state should build for tests");
+        let state = AppState::new().expect("state should build for tests");
 
         let first = limiter
             .check_and_consume(&state, Some(&decision))
@@ -565,7 +565,7 @@ mod tests {
             local_rejection: None,
             allowed_models: None,
         });
-        let state = AppState::new("http://127.0.0.1:1").expect("state should build for tests");
+        let state = AppState::new().expect("state should build for tests");
 
         let first = limiter
             .check_and_consume(&state, Some(&decision))