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/video_tasks/helpers/body.rs

@@ -1,4 +1,4 @@
-use super::*;
+use serde_json::{Map, Value};
 
 pub(crate) fn context_text(context: &Map<String, Value>, key: &str) -> Option<String> {
     context

apps/aether-gateway/src/video_tasks/helpers/path.rs

@@ -1,4 +1,11 @@
-use super::*;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use aether_data::repository::video_tasks::VideoTaskStatus as StoredVideoTaskStatus;
+use uuid::Uuid;
+
+use super::super::{
+    LocalVideoTaskRegistryMutation, LocalVideoTaskStatus, VideoTaskTruthSourceMode,
+};
 
 pub(crate) fn extract_openai_task_id_from_path(path: &str) -> Option<&str> {
     let suffix = path.strip_prefix("/v1/videos/")?;

apps/aether-gateway/src/video_tasks/helpers/transport.rs

@@ -1,4 +1,23 @@
-use super::*;
+use std::collections::BTreeMap;
+
+use aether_contracts::ExecutionPlan;
+use aether_data::repository::video_tasks::{
+    StoredVideoTask, VideoTaskStatus as StoredVideoTaskStatus,
+};
+use serde_json::{Map, Value};
+
+use super::super::{
+    LocalVideoTaskFollowUpPlan, LocalVideoTaskPersistence, LocalVideoTaskStatus,
+    LocalVideoTaskTransport,
+};
+use crate::gateway::provider_transport::{
+    resolve_local_gemini_auth, resolve_local_standard_auth, resolve_transport_execution_timeouts,
+    supports_local_gemini_transport, supports_local_standard_transport,
+    GatewayProviderTransportSnapshot,
+};
+use crate::gateway::GatewayControlAuthContext;
+
+use super::{context_text, non_empty_owned};
 
 impl LocalVideoTaskTransport {
     pub(crate) fn from_plan(plan: &ExecutionPlan) -> Option<Self> {