feat: 引入 Rust executor/gateway sidecar 及 Python 侧双后端适配

- 新增 Rust workspace crates: aether-contracts, aether-executor, aether-gateway
- aether-executor: 支持 Unix Socket/TCP 双传输模式，处理同步/流式上游请求
- aether-gateway: 作为本地主入口代理，集成 /api/internal/gateway/resolve 认证预解析
- Python 侧新增 ExecutionPlan 契约和 RustExecutorClient，各 handler 支持
  executor_backend=rust 时将可序列化请求转发给 Rust executor 执行
- 重构 dev.sh 支持 executor/gateway 进程编排与生命周期管理
- 新增 internal gateway 路由，提供 resolve/passthrough 端点
- handler 层(chat/cli/video/endpoint_checker 等)全面适配 Rust executor 回退逻辑
- pipeline 层支持 trusted auth context 跳过重复认证
- 新增 Rust CI workflow 及对应测试用例

tests/unit/test_executor_config.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+import pytest
+
+from src.config.settings import Config
+
+
+def test_executor_config_defaults_to_rust_and_unix_socket(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    for key in (
+        "EXECUTOR_BACKEND",
+        "EXECUTOR_TRANSPORT",
+        "EXECUTOR_SOCKET_PATH",
+        "EXECUTOR_BASE_URL",
+        "EXECUTOR_REQUEST_TIMEOUT",
+        "HTTP_REQUEST_TIMEOUT",
+    ):
+        monkeypatch.delenv(key, raising=False)
+
+    cfg = Config()
+
+    assert cfg.executor_backend == "rust"
+    assert cfg.executor_transport == "unix_socket"
+    assert cfg.executor_socket_path == "/tmp/aether-executor.sock"
+    assert cfg.executor_base_url == "http://127.0.0.1:5219"
+    assert cfg.executor_request_timeout == cfg.http_request_timeout
+
+
+def test_executor_config_accepts_env_override(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("EXECUTOR_BACKEND", "RUST")
+    monkeypatch.setenv("EXECUTOR_TRANSPORT", "TCP")
+    monkeypatch.setenv("EXECUTOR_SOCKET_PATH", "/var/run/aether.sock")
+    monkeypatch.setenv("EXECUTOR_BASE_URL", "http://127.0.0.1:9311")
+    monkeypatch.setenv("EXECUTOR_REQUEST_TIMEOUT", "12.5")
+
+    cfg = Config()
+
+    assert cfg.executor_backend == "rust"
+    assert cfg.executor_transport == "tcp"
+    assert cfg.executor_socket_path == "/var/run/aether.sock"
+    assert cfg.executor_base_url == "http://127.0.0.1:9311"
+    assert cfg.executor_request_timeout == 12.5