feat(auth): add remember me option with persistent DB sessions

app/templates/login.html

@@ -11,6 +11,9 @@
         <input type="text" name="username" required autofocus>
         <label>密码</label>
         <input type="password" name="password" required>
+        <label class="checkbox-label" style="margin-top:1rem;display:flex;align-items:center;gap:.4rem;cursor:pointer">
+            <input type="checkbox" name="remember_me" style="width:auto;margin:0"> 记住我
+        </label>
         <button type="submit" class="btn btn-primary">登录</button>
     </form>
     <p class="auth-link">没有账号？<a href="/register">注册</a></p>