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/api/admin/stats/comparison.py

@@ -0,0 +1,142 @@
+"""Admin comparison stats routes."""
+
+from __future__ import annotations
+
+from datetime import date, timedelta
+from typing import Any, Literal
+
+from fastapi import APIRouter, Depends, HTTPException, Query, Request
+from sqlalchemy.orm import Session
+
+from src.api.base.admin_adapter import AdminApiAdapter
+from src.api.base.context import ApiRequestContext
+from src.config.constants import CacheTTL
+from src.database import get_db
+from src.services.system.stats_aggregator import AggregatedStats, StatsFilter, query_stats_hybrid
+from src.services.system.time_range import TimeRangeParams
+from src.utils.cache_decorator import cache_result
+
+from .common import pipeline
+
+router = APIRouter()
+
+
+class AdminComparisonAdapter(AdminApiAdapter):
+    def __init__(
+        self,
+        current_start: date,
+        current_end: date,
+        comparison_type: Literal["period", "year"],
+        timezone_name: str | None,
+        tz_offset_minutes: int | None,
+    ) -> None:
+        self.current_start = current_start
+        self.current_end = current_end
+        self.comparison_type = comparison_type
+        self.timezone_name = timezone_name
+        self.tz_offset_minutes = tz_offset_minutes
+
+    @cache_result(
+        key_prefix="admin:stats:comparison",
+        ttl=CacheTTL.ADMIN_USAGE_AGGREGATION,
+        user_specific=False,
+        vary_by=[
+            "current_start",
+            "current_end",
+            "comparison_type",
+            "timezone_name",
+            "tz_offset_minutes",
+        ],
+    )
+    async def handle(self, context: ApiRequestContext) -> Any:  # type: ignore[override]
+        if self.current_start > self.current_end:
+            raise HTTPException(status_code=400, detail="current_start must be <= current_end")
+
+        days = (self.current_end - self.current_start).days + 1
+
+        def _safe_year_shift(value: date) -> date:
+            try:
+                return value.replace(year=value.year - 1)
+            except ValueError:
+                return value.replace(year=value.year - 1, day=28)
+
+        if self.comparison_type == "period":
+            comparison_end = self.current_start - timedelta(days=1)
+            comparison_start = comparison_end - timedelta(days=days - 1)
+        else:
+            comparison_start = _safe_year_shift(self.current_start)
+            comparison_end = _safe_year_shift(self.current_end)
+
+        current_range = TimeRangeParams(
+            start_date=self.current_start,
+            end_date=self.current_end,
+            timezone=self.timezone_name,
+            tz_offset_minutes=self.tz_offset_minutes or 0,
+        ).validate_and_resolve()
+        comparison_range = TimeRangeParams(
+            start_date=comparison_start,
+            end_date=comparison_end,
+            timezone=self.timezone_name,
+            tz_offset_minutes=self.tz_offset_minutes or 0,
+        ).validate_and_resolve()
+
+        current_stats = query_stats_hybrid(context.db, current_range, filters=StatsFilter())
+        comparison_stats = query_stats_hybrid(context.db, comparison_range, filters=StatsFilter())
+
+        def _stats_payload(stats: AggregatedStats) -> dict[str, Any]:
+            total_tokens = (
+                stats.input_tokens
+                + stats.output_tokens
+                + stats.cache_creation_tokens
+                + stats.cache_read_tokens
+            )
+            return {
+                "total_requests": stats.total_requests,
+                "total_tokens": total_tokens,
+                "total_cost": float(stats.total_cost),
+                "actual_total_cost": float(stats.actual_total_cost),
+                "avg_response_time_ms": float(stats.avg_response_time_ms),
+                "error_requests": stats.error_requests,
+            }
+
+        def _pct_change(current: float, previous: float) -> float | None:
+            if previous == 0:
+                return None if current != 0 else 0.0
+            return round((current - previous) / previous * 100, 2)
+
+        current_payload = _stats_payload(current_stats)
+        comparison_payload = _stats_payload(comparison_stats)
+        changes = {
+            key: _pct_change(float(current_payload[key]), float(comparison_payload[key]))
+            for key in current_payload.keys()
+        }
+
+        return {
+            "current": current_payload,
+            "comparison": comparison_payload,
+            "change_percent": changes,
+            "current_start": self.current_start.isoformat(),
+            "current_end": self.current_end.isoformat(),
+            "comparison_start": comparison_start.isoformat(),
+            "comparison_end": comparison_end.isoformat(),
+        }
+
+
+@router.get("/comparison")
+async def get_comparison(
+    request: Request,
+    db: Session = Depends(get_db),
+    current_start: date = Query(...),
+    current_end: date = Query(...),
+    comparison_type: Literal["period", "year"] = Query("period"),
+    timezone_name: str | None = Query(None, alias="timezone"),
+    tz_offset_minutes: int | None = Query(0),
+) -> Any:
+    adapter = AdminComparisonAdapter(
+        current_start=current_start,
+        current_end=current_end,
+        comparison_type=comparison_type,
+        timezone_name=timezone_name,
+        tz_offset_minutes=tz_offset_minutes,
+    )
+    return await pipeline.run(adapter=adapter, http_request=request, db=db, mode=adapter.mode)