fix: 实机验证发现的七个缺陷

部署与时区
- client/.env.production 写死 REACT_APP_API_URL=/api。之前没有这个文件，
  构建靠命令行临时传参，一旦忘了就把开发默认值 localhost:5000 打进包里，
  部署后整站 Network Error。
- 新增 lib/day.ts，所有日期改用本地日历日。原先用 toISOString() 取的是 UTC 日期，
  在 UTC+8 每天前 8 小时都会少查一天——当天的数据佳明已经有了，应用却够不到。

界面
- 覆盖 Framework7 9 给 .navbar .left/.right 加的 frosted pill，
  就是各页右上角和返回键旁边那个半透明椭圆。
- .metric-tab 显式 width:auto。F7 把每个 button 渲染成整宽块元素，
  运动详情的四个 Tab 因此竖着堆成四行。
- 主要收益为 UNKNOWN 时不显示该区块，那是「没有结论」的哨兵值。

正确性
- 心率区间百分比改用整次运动时长作分母。原先除以「落在区间内的总时长」，
  把低于区间 1 的时间挤掉了：44:06 的登山里区间 1 占 23:03，
  手表显示 52%，我算成了 90%。现在对上了。

性能
- 按进程缓存已认证的 Garmin 会话（15 分钟 TTL）。实测 _connect 单次 11 秒，
  而七个数据接口加起来才 4 秒——瓶颈全在每次重新认证。
  冷启 16s → 热 7s → 命中缓存 0.8s，不再撞客户端超时。
- get_activity_details 的 maxchart 由 2000 降到 500，反正写入时抽稀到 300。
- 重新绑定账号时丢弃缓存会话。

删除前端重做前遗留的 5 个无引用页面文件。

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

backend/services/garmin.py

@@ -123,12 +123,44 @@ def save_token(user_id, token, garmin_email=None):
                f"ON CONFLICT(user_id) DO UPDATE SET {updates}")
     execute(sql, [user_id, token, garmin_email,
                   datetime.datetime.utcnow().isoformat(timespec="seconds")])
+    # A re-bind means the old session is stale; the next call must build a
+    # fresh one rather than keep using the session the old token minted.
+    forget_client(user_id)
 
 
 def has_token(user_id):
     return load_token(user_id) is not None
 
 
+# An authenticated client, reused across requests in this process.
+#
+# Building one costs ~11s against Garmin — loading the token, refreshing the
+# OAuth2 grant and fetching the profile — which dwarfed the ~4s of actual data
+# fetching behind an activity-detail request. The session is a requests.Session
+# underneath, so it is reusable; it is dropped after CLIENT_TTL so a refreshed
+# or revoked token is picked up rather than being cached indefinitely.
+CLIENT_TTL_SECONDS = 900
+_clients = {}
+_clients_lock = threading.Lock()
+
+
+def _cached_client(user_id):
+    entry = _clients.get(user_id)
+    if entry and (datetime.datetime.utcnow() - entry[1]).total_seconds() < CLIENT_TTL_SECONDS:
+        return entry[0]
+    return None
+
+
+def _cache_client(user_id, client):
+    if user_id:
+        _clients[user_id] = (client, datetime.datetime.utcnow())
+
+
+def forget_client(user_id):
+    """Drop the cached session — call after re-binding an account."""
+    _clients.pop(user_id, None)
+
+
 def _connect(creds, user_id=None):
     """Obtain a logged-in Garmin client.
 
@@ -138,6 +170,12 @@ def _connect(creds, user_id=None):
     "EOFError: EOF when reading a line"). Tokens are minted once by
     `garmin_login.py`, which runs in a terminal where a code can be typed.
     """
+    if user_id:
+        with _clients_lock:
+            cached = _cached_client(user_id)
+        if cached is not None:
+            return cached
+
     Garmin = _import_garmin()
     client = Garmin(is_cn=_is_cn())
 
@@ -150,6 +188,8 @@ def _connect(creds, user_id=None):
         # garminconnect builds most of its URLs from display_name, so leaving
         # it unset sends every request to ".../None".
         client.display_name = client.garth.profile["displayName"]
+        with _clients_lock:
+            _cache_client(user_id, client)
         return client
 
     if not creds.get("garminPassword"):
@@ -167,6 +207,8 @@ def _connect(creds, user_id=None):
             "系统会提示你输入验证码。"
         ) from e
     _use_api_user_agent(client)
+    with _clients_lock:
+        _cache_client(user_id, client)
     return client
 
 
@@ -519,8 +561,10 @@ def _build_detail(client, activity_id):
     rest of the page intact rather than fail the request.
     """
     summary = _safe(lambda: client.get_activity_evaluation(activity_id), {}) or {}
+    # 500 is already more samples than the 300 we keep, and asking for 2000
+    # triples the payload for points that get thinned away anyway.
     details = _safe(
-        lambda: client.get_activity_details(activity_id, maxchart=2000, maxpoly=0), {}
+        lambda: client.get_activity_details(activity_id, maxchart=500, maxpoly=0), {}
     ) or {}
 
     return {