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/execution_runtime/mod.rs

@@ -251,7 +251,9 @@ pub(crate) fn append_execution_contract_fields_to_value(
 
 #[cfg(test)]
 mod tests {
-    use super::*;
+    use super::{
+        append_execution_contract_fields_to_value, ConversionMode, ExecutionStrategy,
+    };
     use serde_json::json;
 
     #[test]

apps/aether-gateway/src/execution_runtime/stream.rs

@@ -32,7 +32,7 @@ pub(crate) async fn maybe_execute_via_execution_runtime_stream(
     #[cfg(test)]
     {
         if state
-            .test_remote_execution_runtime_base_url()
+            .execution_runtime_override_base_url()
             .unwrap_or_default()
             .is_empty()
             && parts.method != http::Method::POST

apps/aether-gateway/src/execution_runtime/stream/execution.rs

@@ -98,7 +98,7 @@ pub(crate) async fn execute_execution_runtime_stream(
     #[cfg(test)]
     {
         let remote_execution_runtime_base_url = state
-            .test_remote_execution_runtime_base_url()
+            .execution_runtime_override_base_url()
             .unwrap_or_default();
         if remote_execution_runtime_base_url.trim().is_empty() {
             let execution = match DirectSyncExecutionRuntime::new()

apps/aether-gateway/src/execution_runtime/sync.rs

@@ -38,7 +38,7 @@ pub(crate) async fn maybe_execute_via_execution_runtime_sync(
     #[cfg(test)]
     {
         if state
-            .test_remote_execution_runtime_base_url()
+            .execution_runtime_override_base_url()
             .unwrap_or_default()
             .is_empty()
             && parts.method != http::Method::POST

apps/aether-gateway/src/execution_runtime/sync/execution.rs

@@ -101,7 +101,7 @@ pub(crate) async fn execute_execution_runtime_sync(
     #[cfg(test)]
     let result = {
         let remote_execution_runtime_base_url = state
-            .test_remote_execution_runtime_base_url()
+            .execution_runtime_override_base_url()
             .unwrap_or_default();
         if remote_execution_runtime_base_url.trim().is_empty() {
             match DirectSyncExecutionRuntime::new()

apps/aether-gateway/src/execution_runtime/transport.rs

@@ -216,7 +216,7 @@ pub(crate) async fn execute_sync_plan(
     #[cfg(test)]
     {
         let remote_execution_runtime_base_url = state
-            .test_remote_execution_runtime_base_url()
+            .execution_runtime_override_base_url()
             .unwrap_or_default();
         if !remote_execution_runtime_base_url.trim().is_empty() {
             return execute_sync_plan_via_remote_execution_runtime(