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/pool/cost_tracker.py

@@ -0,0 +1,66 @@
+"""Rolling-window cost tracking for the Account Pool.
+
+Each key has a configurable token budget per rolling window (e.g. 5 hours).
+When the budget is exhausted the key is marked as unschedulable by the pool
+manager.  A "soft threshold" (default 80 %) causes the pool to *prefer*
+other keys but still allows traffic if no alternatives exist.
+
+All state is stored in Redis sorted sets via :mod:`redis_ops`.
+"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from src.services.provider.pool import redis_ops
+
+if TYPE_CHECKING:
+    from src.services.provider.pool.config import PoolConfig
+
+
+async def record_usage(
+    provider_id: str,
+    key_id: str,
+    tokens: int,
+    config: PoolConfig,
+) -> None:
+    """Record *tokens* used by *key_id* in the rolling cost window."""
+    if tokens <= 0:
+        return
+    if config.cost_limit_per_key_tokens is None:
+        return  # cost tracking disabled
+    await redis_ops.add_cost_entry(provider_id, key_id, tokens, config.cost_window_seconds)
+
+
+async def get_window_usage(
+    provider_id: str,
+    key_id: str,
+    config: PoolConfig,
+) -> int:
+    """Return total tokens used by *key_id* within the current window."""
+    return await redis_ops.get_cost_window_total(provider_id, key_id, config.cost_window_seconds)
+
+
+async def is_at_limit(
+    provider_id: str,
+    key_id: str,
+    config: PoolConfig,
+) -> bool:
+    """Return ``True`` if the key has exhausted its budget."""
+    if config.cost_limit_per_key_tokens is None:
+        return False
+    total = await get_window_usage(provider_id, key_id, config)
+    return total >= config.cost_limit_per_key_tokens
+
+
+async def is_approaching_limit(
+    provider_id: str,
+    key_id: str,
+    config: PoolConfig,
+) -> bool:
+    """Return ``True`` if the key is above the soft threshold."""
+    if config.cost_limit_per_key_tokens is None:
+        return False
+    total = await get_window_usage(provider_id, key_id, config)
+    threshold = config.cost_limit_per_key_tokens * config.cost_soft_threshold_percent / 100
+    return total >= threshold