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/common.py

@@ -0,0 +1,196 @@
+"""Shared helpers for admin stats routes."""
+
+from __future__ import annotations
+
+import hashlib
+import json
+from datetime import date, datetime, time, timedelta, timezone
+from typing import Any, Literal
+
+from fastapi import HTTPException
+from sqlalchemy import and_, or_
+
+from src.api.base.pipeline import get_pipeline
+from src.config.settings import config
+from src.models.database import Usage
+from src.services.system.time_range import TimeRangeParams
+
+pipeline = get_pipeline()
+
+
+def _apply_admin_default_range(
+    params: TimeRangeParams | None,
+) -> TimeRangeParams | None:
+    """Apply a default range to avoid unbounded scans."""
+    if params is not None:
+        return params
+
+    days = int(getattr(config, "admin_usage_default_days", 0) or 0)
+    if days <= 0:
+        return None
+
+    today = datetime.now(timezone.utc).date()
+    start_date = today - timedelta(days=days - 1)
+    return TimeRangeParams(
+        start_date=start_date,
+        end_date=today,
+        timezone="UTC",
+        tz_offset_minutes=0,
+    ).validate_and_resolve()
+
+
+def _build_time_range_params(
+    start_date: date | None,
+    end_date: date | None,
+    preset: str | None,
+    timezone_name: str | None,
+    tz_offset_minutes: int | None,
+) -> TimeRangeParams | None:
+    if not preset and start_date is None and end_date is None:
+        return None
+    try:
+        return TimeRangeParams(
+            start_date=start_date,
+            end_date=end_date,
+            preset=preset,
+            timezone=timezone_name,
+            tz_offset_minutes=tz_offset_minutes or 0,
+        ).validate_and_resolve()
+    except Exception as exc:
+        raise HTTPException(status_code=400, detail=str(exc)) from exc
+
+
+def _hash_filters(filters: dict[str, Any]) -> str:
+    raw = json.dumps(filters, sort_keys=True, ensure_ascii=False, default=str)
+    return hashlib.sha1(raw.encode("utf-8")).hexdigest()[:16]
+
+
+def _build_time_range_from_days(
+    days: int, timezone_name: str | None, tz_offset_minutes: int | None
+) -> TimeRangeParams:
+    base = TimeRangeParams(
+        preset="today",
+        timezone=timezone_name,
+        tz_offset_minutes=tz_offset_minutes or 0,
+    ).validate_and_resolve()
+    user_today = base.start_date
+    start_date = user_today - timedelta(days=days - 1)
+    return TimeRangeParams(
+        start_date=start_date,
+        end_date=user_today,
+        timezone=timezone_name,
+        tz_offset_minutes=tz_offset_minutes or 0,
+    ).validate_and_resolve()
+
+
+def _linear_regression(values: list[float]) -> tuple[float, float]:
+    n = len(values)
+    if n <= 1:
+        return 0.0, values[0] if values else 0.0
+    xs = list(range(n))
+    sum_x = sum(xs)
+    sum_y = sum(values)
+    sum_x2 = sum(x * x for x in xs)
+    sum_xy = sum(x * y for x, y in zip(xs, values))
+    denom = n * sum_x2 - sum_x * sum_x
+    if denom == 0:
+        return 0.0, values[-1]
+    slope = (n * sum_xy - sum_x * sum_y) / denom
+    intercept = (sum_y - slope * sum_x) / n
+    return slope, intercept
+
+
+def _build_cache_key(
+    leaderboard_type: str,
+    metric: str,
+    time_range: TimeRangeParams | None,
+    filters: dict[str, Any],
+) -> str:
+    start_value = time_range.start_date.isoformat() if time_range else "all"
+    end_value = time_range.end_date.isoformat() if time_range else "all"
+    tz_value = time_range.timezone if time_range else "utc"
+    offset_value = time_range.tz_offset_minutes if time_range else 0
+    return (
+        f"leaderboard:{leaderboard_type}:{metric}:{start_value}:{end_value}:"
+        f"{tz_value}:{offset_value}:{_hash_filters(filters)}"
+    )
+
+
+def _is_today_range(time_range: TimeRangeParams | None) -> bool:
+    if not time_range:
+        return False
+    try:
+        user_today = time_range._get_user_today()
+    except Exception:
+        return False
+    return time_range.end_date == user_today
+
+
+def _split_daily_and_usage_segments(
+    time_range: TimeRangeParams | None,
+    use_daily: bool,
+) -> tuple[tuple[datetime, datetime] | None, list[tuple[datetime, datetime]] | None]:
+    if not time_range:
+        return None, None
+
+    start_utc, end_utc = time_range.to_utc_datetime_range()
+    if not use_daily:
+        return None, [(start_utc, end_utc)]
+
+    complete_dates, head_boundary, tail_boundary = time_range.get_complete_utc_dates()
+    daily_range = None
+    if complete_dates:
+        daily_start = datetime.combine(complete_dates[0], time.min, tzinfo=timezone.utc)
+        daily_end = datetime.combine(
+            complete_dates[-1] + timedelta(days=1), time.min, tzinfo=timezone.utc
+        )
+        daily_range = (daily_start, daily_end)
+
+    usage_segments: list[tuple[datetime, datetime]] = []
+    if head_boundary:
+        usage_segments.append(head_boundary)
+    if tail_boundary:
+        usage_segments.append(tail_boundary)
+
+    if not daily_range and not usage_segments:
+        usage_segments = [(start_utc, end_utc)]
+
+    return daily_range, usage_segments
+
+
+def _apply_usage_time_segments(
+    query: Any, segments: list[tuple[datetime, datetime]] | None
+) -> Any | None:
+    if segments is None:
+        return query
+    if not segments:
+        return None
+
+    conditions = []
+    for start_utc, end_utc in segments:
+        if start_utc >= end_utc:
+            continue
+        conditions.append(and_(Usage.created_at >= start_utc, Usage.created_at < end_utc))
+
+    if not conditions:
+        return None
+
+    return query.filter(or_(*conditions))
+
+
+def _union_queries(queries: list[Any]) -> Any | None:
+    base = None
+    for query in queries:
+        if query is None:
+            continue
+        if base is None:
+            base = query
+        else:
+            base = base.union_all(query)
+    return base
+
+
+def _metric_order(
+    metric: Literal["requests", "tokens", "cost"], order: Literal["asc", "desc"], expr: Any
+) -> Any:
+    return expr.asc() if order == "asc" else expr.desc()