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/error_classifier.py

@@ -0,0 +1,70 @@
+"""Error classification helpers for Usage records."""
+
+from __future__ import annotations
+
+from src.core.enums import ErrorCategory
+
+_STATUS_CODE_MAP: dict[int, ErrorCategory] = {
+    400: ErrorCategory.INVALID_REQUEST,
+    401: ErrorCategory.AUTH,
+    403: ErrorCategory.AUTH,
+    404: ErrorCategory.NOT_FOUND,
+    408: ErrorCategory.TIMEOUT,
+    429: ErrorCategory.RATE_LIMIT,
+    500: ErrorCategory.SERVER_ERROR,
+    502: ErrorCategory.SERVER_ERROR,
+    503: ErrorCategory.SERVER_ERROR,
+    504: ErrorCategory.TIMEOUT,
+}
+
+_CONTEXT_LENGTH_PATTERNS = (
+    "context_length_exceeded",
+    "maximum context length",
+    "too many tokens",
+    "input is too long",
+)
+
+_CONTENT_FILTER_PATTERNS = (
+    "content_filter",
+    "content_policy",
+    "safety_block",
+    "blocked by content",
+)
+
+_NETWORK_PATTERNS = ("connection", "network", "dns", "socket")
+
+
+def classify_error(
+    status_code: int | None,
+    error_message: str | None,
+    status: str | None = None,
+) -> ErrorCategory:
+    """Map provider errors to ErrorCategory."""
+    if status and status.lower() == "cancelled":
+        return ErrorCategory.CANCELLED
+
+    if status_code is not None:
+        mapped = _STATUS_CODE_MAP.get(status_code)
+        if mapped:
+            return mapped
+
+    if error_message:
+        msg_lower = error_message.lower()
+        if any(p in msg_lower for p in _CONTEXT_LENGTH_PATTERNS):
+            return ErrorCategory.CONTEXT_LENGTH
+        if any(p in msg_lower for p in _CONTENT_FILTER_PATTERNS):
+            return ErrorCategory.CONTENT_FILTER
+        if "rate limit" in msg_lower or "rate_limit" in msg_lower:
+            return ErrorCategory.RATE_LIMIT
+        if "timeout" in msg_lower or "timed out" in msg_lower:
+            return ErrorCategory.TIMEOUT
+        if any(p in msg_lower for p in _NETWORK_PATTERNS):
+            return ErrorCategory.NETWORK
+
+    if status_code is not None:
+        if status_code >= 500:
+            return ErrorCategory.SERVER_ERROR
+        if status_code >= 400:
+            return ErrorCategory.INVALID_REQUEST
+
+    return ErrorCategory.UNKNOWN