refactor: 移除 Python 后端源码，全面迁移至 Rust gateway 架构

- 删除全部 Python 源码 (src/) 及 Alembic 迁移脚本，归档至 _deprecated_py_src/
- 重构 Rust gateway ai_pipeline: 拆分 planner/finalize 模块，新增 contracts/adaptation 层
- 重组 handlers 模块为 admin/public/proxy/internal/shared 子模块结构
- 新增 executor 模块，引入 Rust 原生数据库迁移 (aether-data/migrations)
- 简化 CI/Docker 构建流程，移除 base image 二级构建，统一为单一 app image
- 移除 Python 相关基础设施文件 (entrypoint.sh, gunicorn_conf.py, Dockerfile.base)

_deprecated_py_src/services/provider/adapters/codex/context.py

@@ -0,0 +1,55 @@
+"""Codex request-scoped context.
+
+Codex only needs a small amount of per-request runtime state that does not belong in
+the outbound payload itself. Today that state is the compact-mode flag used by the
+transport and upstream stream-policy layers.
+"""
+
+from __future__ import annotations
+
+import contextvars
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, slots=True)
+class CodexRequestContext:
+    """Per-request context for the Codex adapter."""
+
+    is_compact: bool = False
+
+
+_codex_request_context: contextvars.ContextVar[CodexRequestContext | None] = contextvars.ContextVar(
+    "codex_request_context",
+    default=None,
+)
+
+
+def set_codex_request_context(ctx: CodexRequestContext | None) -> None:
+    _codex_request_context.set(ctx)
+
+
+def get_codex_request_context() -> CodexRequestContext | None:
+    return _codex_request_context.get()
+
+
+def is_codex_compact_request(*, endpoint_sig: str | None = None) -> bool:
+    """Return whether the current Codex request should use compact semantics.
+
+    Modern configurations use a dedicated ``openai:compact`` endpoint. Older ones may
+    still route compact traffic through ``openai:cli`` and rely on request-scoped
+    context instead.
+    """
+    normalized_sig = str(endpoint_sig or "").strip().lower()
+    if normalized_sig == "openai:compact":
+        return True
+
+    ctx = get_codex_request_context()
+    return bool(ctx and ctx.is_compact)
+
+
+__all__ = [
+    "CodexRequestContext",
+    "get_codex_request_context",
+    "is_codex_compact_request",
+    "set_codex_request_context",
+]