Fix pace sentinel, route map thumbnails, tiled segments, health/dashboard layout

- Pace: FIT 0xFFFF sentinel (65.535 m/s) was stored as avg_speed_ms on every
  activity and lap; add _sanitize_speed() to parser falling back to dist/dur,
  plus a startup SQL migration that fixed 120 activities and 688 laps in-place
- Records: remove swimming from Distance PRs; Route Records rows are clickable
  (navigate to activity), View button removed, small SVG route map per row;
  Segment Records uses same tiled route-card layout as Segments page
- Segments: replace route dropdown with responsive tile grid showing SVG map
  thumbnails; selecting a tile reveals the segment management panel below
- RouteMiniMap: new pure-SVG component (no Leaflet) for route thumbnails,
  decodes polyline and normalises coords into a fixed viewBox
- Health: rename "Avg Heart Rate (day)" → "Heart Rate"; weight chart now
  filters to non-null rows and enables connectNulls + dots for sparse data
- Dashboard: 4-col layout at lg breakpoint so Body Battery sits between weekly
  chart and Health Today; Body Battery card gains a 24-hr sparkline from the
  values[] already present in the health summary response

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

CLAUDE.md

@@ -103,3 +103,13 @@ Required in `.env` (or passed to Docker Compose):
 | `BASE_URL` | Used for PocketID OAuth callback redirect URI |
 | `VITE_MAPBOX_TOKEN` | Optional — enables satellite tile layer |
 | `POCKETID_ISSUER` / `POCKETID_CLIENT_ID` / `POCKETID_CLIENT_SECRET` | Optional OIDC |
+
+## Debugging and troubleshooting
+- The latest build will always be running in docker at ~/milevault_docker with the following container names:
+    `milevault_backend`
+    `milevault_db`
+    `milevault_frontend`
+    `milevault_redis`
+    `milevault_worker`
+- When an issue is highlighted by the user, check the logs on these containers for the error, do not spin up new containers, rectify the issues in ~/milevault where the development is happening
+- Do NOT patch the running files under any circumstances, fix the development files.