feat: PWA支持（manifest+Service Worker缓存+图标，可添加到主屏幕/离线/增量更新）

app/main.py

@@ -11,7 +11,7 @@ from pathlib import Path
 
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import HTMLResponse
+from fastapi.responses import FileResponse, HTMLResponse
 from fastapi.staticfiles import StaticFiles
 from jinja2 import Environment, FileSystemLoader
 from sqlmodel import Session
@@ -64,6 +64,16 @@ def index() -> HTMLResponse:
     return HTMLResponse(html)
 
 
+@app.get("/sw.js", include_in_schema=False)
+def service_worker() -> FileResponse:
+    """Service Worker（置于根路径以使 scope 覆盖全站）"""
+    return FileResponse(
+        STATIC_DIR / "sw.js",
+        media_type="application/javascript",
+        headers={"Service-Worker-Allowed": "/"},
+    )
+
+
 @app.get("/health")
 def health_check() -> dict:
     """健康检查（version 动态读取，便于验证自动更新）"""