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

.github/workflows/rust-ci.yml

@@ -0,0 +1,48 @@
+name: Rust CI
+
+on:
+  push:
+    branches:
+      - master
+      - aether-rust-pioneer
+    paths:
+      - "Cargo.toml"
+      - "crates/**"
+      - "aether-hub/**"
+      - "aether-proxy/**"
+      - ".github/workflows/rust-ci.yml"
+  pull_request:
+    paths:
+      - "Cargo.toml"
+      - "crates/**"
+      - "aether-hub/**"
+      - "aether-proxy/**"
+      - ".github/workflows/rust-ci.yml"
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy
+
+      - name: Rust cache
+        uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: . -> target
+
+      - name: Format
+        run: cargo fmt --all --check
+
+      - name: Clippy
+        run: cargo clippy --workspace --all-targets -- -D warnings
+
+      - name: Test
+        run: cargo test --workspace
+
+      - name: Build
+        run: cargo build --workspace --release