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>

backend/app/api/users.py

@@ -19,7 +19,7 @@ from app.core.security import get_current_user
 from app.core.config import settings
 from app.models.user import (
     User, Activity, ActivityDataPoint, ActivityLap, NamedRoute,
-    RouteSegment, PersonalRecord, HealthMetric, WeightLog, GarminConnectConfig,
+    Segment, SegmentEffort, PersonalRecord, HealthMetric, WeightLog, GarminConnectConfig,
 )
 
 router = APIRouter()
@@ -122,12 +122,13 @@ async def delete_user(
     # Ordered deletes: PersonalRecord and the activity/route child tables have no
     # cascade path from User, so remove them before the parents to avoid FK errors.
     activity_ids = select(Activity.id).where(Activity.user_id == user_id)
-    route_ids = select(NamedRoute.id).where(NamedRoute.user_id == user_id)
+    segment_ids = select(Segment.id).where(Segment.user_id == user_id)
 
     await db.execute(delete(PersonalRecord).where(PersonalRecord.user_id == user_id))
     await db.execute(delete(ActivityLap).where(ActivityLap.activity_id.in_(activity_ids)))
     await db.execute(delete(ActivityDataPoint).where(ActivityDataPoint.activity_id.in_(activity_ids)))
-    await db.execute(delete(RouteSegment).where(RouteSegment.route_id.in_(route_ids)))
+    await db.execute(delete(SegmentEffort).where(SegmentEffort.segment_id.in_(segment_ids)))
+    await db.execute(delete(Segment).where(Segment.user_id == user_id))
     await db.execute(delete(Activity).where(Activity.user_id == user_id))
     await db.execute(delete(NamedRoute).where(NamedRoute.user_id == user_id))
     await db.execute(delete(HealthMetric).where(HealthMetric.user_id == user_id))