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/components/activity/MetricTimeline.jsx

@@ -62,16 +62,21 @@ export default function MetricTimeline({ dataPoints, activeMetrics, metrics, onH
   const domains = useMemo(() => {
     const result = {}
     for (const m of activeMetricConfigs) {
-      const vals = chartData.map(p => p[m.key]).filter(v => v != null)
+      let vals = chartData.map(p => p[m.key]).filter(v => v != null)
       if (!vals.length) continue
+      // Clamp GPS speed outliers (spikes cause absurd pace labels like 0:01/km)
+      if (m.key === 'speed_ms') {
+        const speedCap = sportType === 'cycling' ? 25 : 12
+        vals = vals.filter(v => v > 0 && v <= speedCap)
+        if (!vals.length) continue
+      }
       const min = Math.min(...vals)
       const max = Math.max(...vals)
       const pad = (max - min) * 0.1 || 1
-      // For elevation, don't start from 0 - show actual range
       result[m.key] = [min - pad, max + pad]
     }
     return result
-  }, [chartData, activeMetricConfigs])
+  }, [chartData, activeMetricConfigs, sportType])
 
   if (!chartData.length) {
     return (
@@ -115,6 +120,7 @@ export default function MetricTimeline({ dataPoints, activeMetrics, metrics, onH
                   width={40}
                   tickFormatter={v => {
                     if (metric.key === 'speed_ms') {
+                      if (v <= 0 || v > 25) return ''
                       if (sportType === 'cycling') return `${(v * 3.6).toFixed(0)}`
                       const spm = 1000 / v
                       return `${Math.floor(spm/60)}:${String(Math.floor(spm%60)).padStart(2,'0')}`