Show expected vs actual pace/HR per lap in the Review Queue

Activities recorded from a structured Garmin workout carry a workoutId;
when its steps line up 1:1 with the recorded laps, the per-step target
pace/HR zone is resolved (via a Karvonen lookup for named zones) and stored
on each lap. The Review Queue plots it against the actual per-lap pace/HR
so the user can eyeball whether a run matches its plan while sorting it.

backend/internal/store/migrations/0008_workout_targets.sql

@@ -0,0 +1,12 @@
+-- Structured Garmin workouts (created in Garmin Connect or a training plan
+-- tool) attach a per-step target pace/HR zone. An activity recorded from one
+-- carries that workout's id; when its laps line up 1:1 with the workout's
+-- flattened steps (see internal/sync's alignWorkoutTargets), the expected
+-- band is resolved and stored per lap so the Review Queue can plot expected
+-- vs actual pace/HR without a live Garmin call on every page view.
+ALTER TABLE activities ADD COLUMN workout_id INTEGER;
+
+ALTER TABLE laps ADD COLUMN target_pace_low_mps REAL;
+ALTER TABLE laps ADD COLUMN target_pace_high_mps REAL;
+ALTER TABLE laps ADD COLUMN target_hr_low_bpm REAL;
+ALTER TABLE laps ADD COLUMN target_hr_high_bpm REAL;