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/models/user.py

@@ -28,6 +28,7 @@ class User(Base):
     birth_year = Column(Integer, nullable=True)
     height_cm = Column(Float, nullable=True)
     biological_sex = Column(String(8), nullable=True)   # 'male' | 'female'
+    goal_weight_kg = Column(Float, nullable=True)
 
     # PocketID config (stored per-user so admin can set via UI)
     pocketid_issuer = Column(String(512), nullable=True)
@@ -172,22 +173,45 @@ class NamedRoute(Base):
 
     user = relationship("User", back_populates="named_routes")
     activities = relationship("Activity", back_populates="named_route")
-    segments = relationship("RouteSegment", back_populates="route", cascade="all, delete-orphan")
 
 
-class RouteSegment(Base):
-    __tablename__ = "route_segments"
+class Segment(Base):
+    """A user-defined GPS segment (a stretch of road/trail) matched across activities."""
+    __tablename__ = "segments"
 
     id = Column(Integer, primary_key=True)
-    route_id = Column(Integer, ForeignKey("named_routes.id"), nullable=False, index=True)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=False, index=True)
     name = Column(String(256), nullable=False)
-    start_distance_m = Column(Float, nullable=False)
-    end_distance_m = Column(Float, nullable=False)
-    description = Column(Text, nullable=True)
-    auto_generated = Column(Boolean, default=False)
-    auto_generated_type = Column(String(20), nullable=True)  # '1km' | 'turns' | 'hills'
+    sport_type = Column(String(64), nullable=True)
+    polyline = Column(Text, nullable=True)          # encoded GPS geometry of the segment
+    start_lat = Column(Float, nullable=True)
+    start_lng = Column(Float, nullable=True)
+    end_lat = Column(Float, nullable=True)
+    end_lng = Column(Float, nullable=True)
+    distance_m = Column(Float, nullable=True)
+    bounding_box = Column(JSON, nullable=True)      # {min_lat,max_lat,min_lon,max_lon}
+    created_from_activity_id = Column(Integer, nullable=True)
+    created_at = Column(DateTime(timezone=True), default=now_utc)
 
-    route = relationship("NamedRoute", back_populates="segments")
+    efforts = relationship("SegmentEffort", back_populates="segment", cascade="all, delete-orphan")
+
+
+class SegmentEffort(Base):
+    """One activity's time over a segment."""
+    __tablename__ = "segment_efforts"
+
+    id = Column(Integer, primary_key=True)
+    segment_id = Column(Integer, ForeignKey("segments.id", ondelete="CASCADE"), nullable=False, index=True)
+    activity_id = Column(Integer, ForeignKey("activities.id", ondelete="CASCADE"), nullable=False, index=True)
+    duration_s = Column(Float, nullable=False)
+    achieved_at = Column(DateTime(timezone=True), nullable=True)
+    rank = Column(Integer, nullable=True)           # 1/2/3 for podium, else null
+
+    __table_args__ = (
+        UniqueConstraint("segment_id", "activity_id", name="uq_segment_effort"),
+    )
+
+    segment = relationship("Segment", back_populates="efforts")
 
 
 class PersonalRecord(Base):