Add segments, YTD stats, route matching fixes, body battery layout, pace fix

- Segments page: new /segments route with auto-generate (1km splits, turn
  detection, hill detection), manual segment creation, per-segment performance
  times across matched activities; fixed auth on existing segment endpoints
- YTD distance: new /activities/stats/ytd endpoint; Dashboard replaces
  'Total distance' with 'Running this year' + 'Cycling this year'; Activities
  page shows YTD stats row
- Weekly chart click: clicking a Dashboard bar navigates to Activities filtered
  to that week; Activities reads from/to query params with dismissable chip
- Route matching: add ±2.5% distance gate + 3% relative DTW threshold
  (was flat 80m); tighten candidate pre-filter from 80/120% to 95/105%
- Body battery layout: HR chart and body battery now side-by-side at same
  height on large screens instead of stacked full-width
- Pace display fix: MetricTimeline clamps GPS speed outliers before computing
  Y-axis domain; tick formatter guards against v<=0 or v>25 m/s

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/HealthPage.jsx

@@ -103,7 +103,7 @@ function BodyBatteryChart({ bb }) {
   }))
 
   return (
-    <div className="bg-gray-900 rounded-xl border border-gray-800 p-5 space-y-4">
+    <div className="bg-gray-900 rounded-xl border border-gray-800 p-5 space-y-4 h-full">
       <h3 className="text-sm font-medium text-gray-300">Body Battery</h3>
 
       <div className="flex items-center gap-8">
@@ -340,22 +340,26 @@ function DailySnapshot({ day, avg30, intradayHr, bodyBattery, onOlder, onNewer,
         </div>
       </div>
 
-      {/* 24-hour heart rate chart */}
-      {intradayHr?.length > 0 && (
-        <div className="bg-gray-900 rounded-xl border border-gray-800 p-4">
-          <div className="flex items-center justify-between mb-2">
-            <h3 className="text-sm font-medium text-gray-300">24-hour Heart Rate</h3>
-            {day.avg_hr_day && (
-              <span className="text-xs text-gray-500">avg {Math.round(day.avg_hr_day)} bpm</span>
-            )}
-          </div>
-          <IntradayHrChart values={intradayHr} />
+      {/* 24-hour heart rate chart + body battery (side by side) */}
+      {(intradayHr?.length > 0 || bodyBattery) && (
+        <div className={`grid gap-4 ${intradayHr?.length > 0 && bodyBattery ? 'grid-cols-1 lg:grid-cols-2' : 'grid-cols-1'}`}>
+          {intradayHr?.length > 0 && (
+            <div className="bg-gray-900 rounded-xl border border-gray-800 p-4 flex flex-col">
+              <div className="flex items-center justify-between mb-2">
+                <h3 className="text-sm font-medium text-gray-300">24-hour Heart Rate</h3>
+                {day.avg_hr_day && (
+                  <span className="text-xs text-gray-500">avg {Math.round(day.avg_hr_day)} bpm</span>
+                )}
+              </div>
+              <div className="flex-1 min-h-0">
+                <IntradayHrChart values={intradayHr} />
+              </div>
+            </div>
+          )}
+          <BodyBatteryChart bb={bodyBattery} />
         </div>
       )}
 
-      {/* Body battery */}
-      <BodyBatteryChart bb={bodyBattery} />
-
       {/* Activity strip */}
       <div className="grid grid-cols-2 sm:grid-cols-4 gap-3">