Track moving time vs elapsed time (pause should reduce moving time)

Problem

The recorder sets moving_time === duration (useRecorder.ts), so pausing doesn't reduce moving time. Strava distinguishes moving vs elapsed for pace.

Acceptance

• Track paused intervals; moving_time = elapsed − paused.
• Persist + display both; compute pace from moving_time.

Fixed in 5961939. duration is now wall-clock elapsed (from a startedAtMs anchor) and moving_time is the pause-aware ticker; pace derives from moving time. Pausing also actually pauses now — GPS fixes are ignored while paused, so distance/route/capture progress stop accruing (previously distance kept growing). Both times are persisted (new activities.moving_time column, legacy rows fall back movingTime=duration) and the activity detail page shows Moving Time with an 'Elapsed …' subline when they differ. Verified: a synthetic 10-minute pause gap leaves split paces untouched (scripts/verify-activity-quality.ts).