feat(python): 完成 Python 全量迁移——剩余平台、登录通道与公共层修复

- 新增 5sing/apple/xm/me/qt/lr 平台包与取流实现（含 xm-sign、MissEvan 签名、蜻蜓 HMAC、Apple developer token）
- 新增 wy/kg/tx/lr 登录：扫码、手机号、账密（kg 20028 风控指纹）、cookie 绑定、kg/tx 续期
- request 层：保留多值 Set-Cookie；JSON body 紧凑化（修复 kg 网关验签）；直连不经系统代理（对齐 Node）
- 登录路由统一 Body(embed=True)，修复扫码轮询 422；lifespan 接入登录续期调度
- ruff/format/pyright 全绿；14 平台真实联网与 HTTP 路由验证通过

app/routes/system.py

@@ -0,0 +1,51 @@
+"""系统路由 —— 健康检查与平台能力清单。"""
+
+from __future__ import annotations
+
+import time
+from typing import Any
+
+from app.http.envelope import ok
+from app.sdk import SUPPORTED_SOURCES, support_quality
+from app.sdk.platforms._base import capability_map
+from fastapi import APIRouter, Request
+
+router = APIRouter(tags=["系统"])
+
+
+@router.get(
+    "/health",
+    summary="健康检查",
+    description="返回运行时长与已接入平台数，可用于探活与监控。",
+)
+async def health(request: Request) -> Any:
+    started_at = getattr(request.app.state, "started_at", None) or time.time()
+    return ok(
+        {
+            "status": "ok",
+            "uptime": round(time.time() - started_at),
+            "platforms": len(SUPPORTED_SOURCES),
+        }
+    )
+
+
+@router.get(
+    "/sources",
+    summary="获取支持的平台",
+    description="返回各平台的音质支持与能力（search/url/lyric/pic/boards/hotSearch/songList/"
+    "singer/album/albumSearch/playlist/playlistSearch/playlistCategories/parse/userPlaylist）。"
+    "音质为 SDK 官方直连接口的支持范围。",
+)
+async def sources() -> Any:
+    platforms: list[dict[str, Any]] = []
+    for item in SUPPORTED_SOURCES:
+        module = item["module"]
+        platforms.append(
+            {
+                "id": item["id"],
+                "name": item["name"],
+                "qualities": support_quality.get(item["id"], []),
+                "capabilities": capability_map(module),
+            }
+        )
+    return ok({"platforms": platforms})