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/usage/events.py

@@ -0,0 +1,125 @@
+"""
+Usage 事件定义与序列化工具（用于 Redis Streams）
+"""
+
+from __future__ import annotations
+
+import json
+import time
+from dataclasses import dataclass
+from enum import Enum
+from typing import Any
+
+import msgpack
+from msgpack.exceptions import OutOfData
+
+USAGE_EVENT_VERSION = 1
+
+
+class UsageEventType(str, Enum):
+    STREAMING = "streaming"
+    COMPLETED = "completed"
+    FAILED = "failed"
+    CANCELLED = "cancelled"
+
+
+def now_ms() -> int:
+    return int(time.time() * 1000)
+
+
+def _sanitize_value(value: Any) -> Any:
+    if value is None or isinstance(value, (str, int, float, bool)):
+        return value
+    if isinstance(value, dict):
+        return {str(k): _sanitize_value(v) for k, v in value.items()}
+    if isinstance(value, list):
+        return [_sanitize_value(item) for item in value]
+    return str(value)
+
+
+def sanitize_payload(data: dict[str, Any]) -> dict[str, Any]:
+    return {str(k): _sanitize_value(v) for k, v in data.items()}
+
+
+def _decode_payload(raw: Any) -> dict[str, Any]:
+    """兼容解码：优先 msgpack，回退旧 JSON。
+
+    统一将输入归一化为 bytes 后走单一解码路径：msgpack → JSON fallback。
+    str 输入来自 decode_responses=True + surrogateescape 的 Redis 客户端，
+    通过 surrogateescape 可无损还原回原始 bytes。
+    """
+    if isinstance(raw, str):
+        raw = raw.encode("utf-8", errors="surrogateescape")
+
+    if not isinstance(raw, (bytes, bytearray, memoryview)):
+        raise ValueError("Invalid payload field in usage event")
+
+    payload_bytes = bytes(raw)
+
+    # 新格式：msgpack
+    try:
+        payload = msgpack.unpackb(payload_bytes, raw=False)
+    except (ValueError, OutOfData, TypeError):
+        # 兼容旧格式：JSON bytes（含 surrogateescape 还原后的纯 UTF-8 JSON）
+        try:
+            payload = json.loads(payload_bytes.decode("utf-8"))
+        except (UnicodeDecodeError, json.JSONDecodeError, TypeError) as exc:
+            raise ValueError("Invalid payload field in usage event") from exc
+
+    if not isinstance(payload, dict):
+        raise ValueError("Invalid payload field in usage event")
+    return payload
+
+
+@dataclass
+class UsageEvent:
+    event_type: UsageEventType
+    request_id: str
+    timestamp_ms: int
+    data: dict[str, Any]
+
+    def to_stream_fields(self) -> dict[str, bytes]:
+        """序列化为 Redis Stream 字段。
+
+        该函数返回 bytes payload，要求读写 usage queue 的 Redis 客户端使用
+        decode_responses=True，并以 surrogateescape 做 UTF-8 编解码，
+        以保证 bytes <-> str 往返无损。
+        """
+        payload = {
+            "v": USAGE_EVENT_VERSION,
+            "type": self.event_type.value,
+            "request_id": self.request_id,
+            "timestamp_ms": self.timestamp_ms,
+            # 兜底清洗，避免 metadata 中混入非 JSON 类型导致队列写入失败。
+            "data": sanitize_payload(self.data),
+        }
+        return {"payload": msgpack.packb(payload, use_bin_type=True)}
+
+    @classmethod
+    def from_stream_fields(cls, fields: dict[str, Any]) -> UsageEvent:
+        raw = fields.get("payload")
+        if not raw:
+            raise ValueError("Missing payload field in usage event")
+        payload = _decode_payload(raw)
+        event_type = UsageEventType(payload["type"])
+        return cls(
+            event_type=event_type,
+            request_id=payload["request_id"],
+            timestamp_ms=int(payload.get("timestamp_ms", 0)),
+            data=payload.get("data", {}) or {},
+        )
+
+
+def build_usage_event(
+    *,
+    event_type: UsageEventType,
+    request_id: str,
+    data: dict[str, Any],
+    timestamp_ms: int | None = None,
+) -> UsageEvent:
+    return UsageEvent(
+        event_type=event_type,
+        request_id=request_id,
+        timestamp_ms=timestamp_ms or now_ms(),
+        data=data,
+    )