feat(sync): 运动详情改为同步入库，详情页只读本地

按需回源是错的：点一次运动要等七个 Garmin 接口，网络好的时候慢，
网络差的时候直接超时（实测公网下 Network Error）。

- sync_data 顺带补齐缺详情的运动
- POST /api/garmin/sync-details 后台补齐存量，GET 查进度
- 详情页只读本地库；没有就提示去同步，不再回源
- 同步页新增「补齐运动详情」按钮，带进度

身体年龄：加入公开的阻尼系数
- 34 岁 VO₂max 46 原本算出 21 岁。不是算错，是方法本身会饱和：
  人与人之间的 VO₂max 标准差约 7，而年龄每年只带来约 0.35 的衰减，
  于是稍微能练的人都会撞到参考表最年轻一档。
- 按 50% 向实际年龄收拢，收敛范围 ±20 → ±12 岁，同一算例现在给 27 岁。
- 去掉「高于最年轻一档按 20 岁计」的硬地板，那是一道正好落在用户身上的悬崖。
- 界面同时显示未收拢的原始值，阻尼系数写进评分依据。

路由：为每个路径补无斜杠别名
- F7 写地址栏时去掉尾斜杠，于是 /daily/ 在地址栏是 /daily，
  而那个地址匹配不到任何路由，刷新或分享就落到「找不到页面」。

布局：让页面结构上无法被撑宽
- 网格改用 minmax(min(210px,100%),1fr)：裸的 minmax(210px,1fr) 允许
  两列加起来超过窄屏宽度，第二张卡就被切掉在屏幕外。
- .ring-row 用 minmax(0,1fr)，1fr 会以 min-content 兜底，一句长说明就能
  把整行顶宽。
- .page-inner 加 overflow-x: clip。
- html/body 用 100dvh：手机浏览器把自己的地址栏盖在布局视口上，
  100% 高的应用会把底部 Tab 栏顶到它们下面——对用户来说就是没有 Tab 栏。

测试：新增 122 项（设置 44、身体年龄 44、运动详情 42），全量 446 项通过。

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

backend/services/fitness_age.py

@@ -10,12 +10,11 @@ step it took is returned alongside the number for the UI to display.
 Method
 ------
 1. Base age from VO2max: the age at which the user's VO2max equals the median
-   for their sex, interpolated over the reference table below. VO2max is the
-   single strongest fitness predictor and is what Garmin's own model leans on.
+   for their sex, interpolated over the reference table below, then damped
+   towards their real age — see VO2_DAMPING for why that damping has to exist.
 2. Resting-heart-rate adjustment, relative to a 60 bpm reference.
 3. BMI adjustment, relative to the healthy 18.5–24.9 band.
-4. Clamped to within 20 years of chronological age — beyond that the
-   extrapolation says more about the table's edges than about the person.
+4. Clamped to within MAX_DEVIATION years of chronological age.
 
 Reference values are 50th-percentile VO2max (ml/kg/min) by age and sex, from
 the widely published ACSM / Cooper Institute cardiorespiratory fitness norms.
@@ -37,7 +36,15 @@ BMI_LOW, BMI_HIGH = 18.5, 24.9
 BMI_YEARS_PER_UNIT = 0.5
 BMI_CAP = 5.0
 
-MAX_DEVIATION = 20.0        # years either side of chronological age
+# Individual VO2max varies far more between people (SD ~7 ml/kg/min) than it
+# declines with age (~0.35 ml/kg/min per year), so a raw "what age is this
+# VO2max the median for" answer swings enormously: a VO2max of 46 at 34 reads
+# as 20, because it genuinely is the median for a 20-year-old. Published
+# fitness-age calculators all compress that swing; this one does too, by an
+# explicit factor that is shown to the user rather than buried.
+VO2_DAMPING = 0.5
+
+MAX_DEVIATION = 12.0        # years either side of chronological age
 AGE_FLOOR, AGE_CEILING = 20.0, 85.0
 
 # Rendered verbatim in 设置 → 评分依据. Kept here, next to the constants it
@@ -52,8 +59,12 @@ BASIS = {
         {
             "name": "基准：VO₂max 对应年龄",
             "detail": "找出你的 VO₂max 相当于同性别人群哪个年龄的中位水平，"
-                      "在参考表上线性插值；高于最年轻一档时按 20 岁计，"
-                      "参考表再往上说明不了更多。",
+                      f"在参考表上线性插值，再按 {VO2_DAMPING:.0%} 的阻尼"
+                      "向实际年龄收拢。"
+                      "不收拢的话，个体差异会淹没年龄效应——人与人之间的 "
+                      "VO₂max 标准差约 7 ml/kg/min，而年龄每年只带来约 0.35 "
+                      "的衰减，于是稍微能练的人都会算出 20 岁。"
+                      "界面上同时显示未收拢的原始值。",
             "source": "ACSM / Cooper Institute 心肺适能人群常模（50 百分位）",
         },
         {
@@ -84,16 +95,17 @@ BASIS = {
 def _interpolate_age(vo2, table):
     """The age whose median VO2max equals `vo2`.
 
-    Above the youngest reference row the answer is simply "fitter than the
-    median 25-year-old", and the table cannot say more: extrapolating its slope
-    there gives absurdities (VO2max 48 reads as an eleven-year-old), so the
-    result floors instead.
+    Both ends continue along the nearest segment's slope. A hard floor here
+    would put everyone above the youngest row at exactly the same age, which
+    is a cliff precisely where the app's users sit; the damping applied to the
+    result afterwards is what keeps the extrapolation from running away.
     """
     first_age, first_vo2 = table[0]
     last_age, last_vo2 = table[-1]
 
     if vo2 >= first_vo2:
-        return AGE_FLOOR
+        slope = (table[1][0] - first_age) / (table[1][1] - first_vo2)
+        return first_age + (vo2 - first_vo2) * slope
     if vo2 <= last_vo2:
         slope = (last_age - table[-2][0]) / (last_vo2 - table[-2][1])
         return last_age + (vo2 - last_vo2) * slope
@@ -122,11 +134,19 @@ def estimate(*, age, sex, vo2max, resting_hr=None, bmi=None):
         return {"value": None, "missing": missing, "basis": BASIS}
 
     table = VO2_MEDIAN[sex]
-    base = _interpolate_age(float(vo2max), table)
+    chronological = float(age)
+    raw = _interpolate_age(float(vo2max), table)
+
+    # Pull the raw figure back towards the user's real age by the damping
+    # factor. Reported alongside the raw value so the compression is visible.
+    base = chronological + (raw - chronological) * VO2_DAMPING
+
     steps = [{
         "label": "VO₂max 基准",
         "input": f"{float(vo2max):.0f} ml/kg/min",
         "years": round(base, 1),
+        "raw": round(raw, 1),
+        "damping": VO2_DAMPING,
         "kind": "base",
     }]
 
@@ -160,7 +180,6 @@ def estimate(*, age, sex, vo2max, resting_hr=None, bmi=None):
             "kind": "adjust",
         })
 
-    chronological = float(age)
     clamped = max(chronological - MAX_DEVIATION,
                   min(chronological + MAX_DEVIATION, total))
     clamped = max(AGE_FLOOR, min(AGE_CEILING, clamped))