Batch 1: dashboard, maps, segments rewrite, health, sync UX

Fixes:
- Dashboard: featured most-recent activity card with map + stats
- Maps default to Street; preferCanvas + larger tile buffer for smoother pan/zoom
- Running cadence as colour-banded dots + 165 spm guide line
- Routes: inline row expansion, rename (PATCH /routes/{id}), podium + deltas, tiled map
- Records: remove reversed pace Y-axis
- Profile: remove resting HR; add goal weight
- Health: snapshot weight carry-forward; VO2 trend axis 30-70;
  weight goal line + kg/st-lb toggle + axis max; sleep 8h/avg lines
- Garmin sync progress moved to global store with persistent floating bar

Features:
- Speed-coloured activity route (default) with Speed/Solid toggle
- GPS-geometry segments: draw on map, match across all activities,
  1st/2nd/3rd leaderboard + podium badges (replaces old distance segments)
- Lap bests: best time per lap across a route + delta column
- Body Battery: highlight activity time windows

Schema: users.goal_weight_kg ALTER; new segments/segment_efforts tables.
Removes RouteSegment, the Segments page, and segment-bests endpoints.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/App.jsx

@@ -8,7 +8,6 @@ import ActivitiesPage from './pages/ActivitiesPage'
 import ActivityDetailPage from './pages/ActivityDetailPage'
 import HealthPage from './pages/HealthPage'
 import RoutesPage from './pages/RoutesPage'
-import SegmentsPage from './pages/SegmentsPage'
 import RecordsPage from './pages/RecordsPage'
 import UploadPage from './pages/UploadPage'
 import ProfilePage from './pages/ProfilePage'
@@ -36,7 +35,6 @@ export default function App() {
         <Route path="activities/:id" element={<ActivityDetailPage />} />
         <Route path="health" element={<HealthPage />} />
         <Route path="routes" element={<RoutesPage />} />
-        <Route path="segments" element={<SegmentsPage />} />
         <Route path="records" element={<RecordsPage />} />
         <Route path="upload" element={<UploadPage />} />
         <Route path="profile" element={<ProfilePage />} />