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/gateway/tests/usage/direct.rs

@@ -1,4 +1,13 @@
-use super::*;
+use super::{
+    any, build_router_with_state, build_state_with_execution_runtime_override, hash_api_key, json,
+    sample_local_openai_auth_snapshot, sample_local_openai_candidate_row,
+    sample_local_openai_endpoint, sample_local_openai_key, sample_local_openai_provider,
+    start_server, Arc, Body, DEVELOPMENT_ENCRYPTION_KEY, GatewayDataState, HeaderValue, Json,
+    InMemoryAuthApiKeySnapshotRepository, InMemoryMinimalCandidateSelectionReadRepository,
+    InMemoryProviderCatalogReadRepository, InMemoryRequestCandidateRepository,
+    InMemoryUsageReadRepository, Request, Response, Router, StatusCode, TRACE_ID_HEADER,
+    UsageReadRepository, UsageRuntimeConfig,
+};
 
 #[tokio::test]
 async fn gateway_records_usage_for_execution_runtime_sync_when_runtime_enabled() {
@@ -53,7 +62,7 @@ async fn gateway_records_usage_for_execution_runtime_sync_when_runtime_enabled()
     let (upstream_url, upstream_handle) = start_server(upstream).await;
     let (execution_runtime_url, execution_runtime_handle) = start_server(execution_runtime).await;
     let gateway_state =
-        build_state_with_test_remote_execution_runtime(upstream_url.clone(), execution_runtime_url)
+        build_state_with_execution_runtime_override(execution_runtime_url)
             .with_data_state_for_tests(
                 GatewayDataState::with_auth_candidate_selection_provider_catalog_request_candidates_and_usage_for_tests(
                     auth_repository,
@@ -188,13 +197,12 @@ async fn gateway_records_usage_for_execution_runtime_stream_when_runtime_enabled
 
     let (upstream_url, upstream_handle) = start_server(upstream).await;
     let (execution_runtime_url, execution_runtime_handle) = start_server(execution_runtime).await;
-    let gateway_state =
-        build_state_with_test_remote_execution_runtime(upstream_url.clone(), execution_runtime_url)
-            .with_usage_data_repository_for_tests(usage_repository.clone())
-            .with_usage_runtime_for_tests(UsageRuntimeConfig {
-                enabled: true,
-                ..UsageRuntimeConfig::default()
-            });
+    let gateway_state = build_state_with_execution_runtime_override(execution_runtime_url)
+        .with_usage_data_repository_for_tests(usage_repository.clone())
+        .with_usage_runtime_for_tests(UsageRuntimeConfig {
+            enabled: true,
+            ..UsageRuntimeConfig::default()
+        });
     let gateway = build_router_with_state(gateway_state);
     let (gateway_url, gateway_handle) = start_server(gateway).await;