Build the Review Queue chart's actual trace from per-second samples, not lap averages

A lap can span many minutes, so plotting one flat value per lap hid real
within-lap variation -- a single-lap hill repeat rendered as a dead-flat
line despite the pace/HR swinging throughout it. The actual pace/HR trace
now comes from activity_samples (per-second telemetry) when available,
looking up each sample's enclosing lap only for the target band/phase
color. Falls back to the previous lap-stepped rendering when an activity
has no samples.

frontend/src/types/api.ts

@@ -62,6 +62,15 @@ export interface Lap {
   RawJSON: string;
 }
 
+export interface Sample {
+  ElapsedSeconds: number;
+  TimestampMs: number;
+  HeartRate: number | null;
+  SpeedMps: number | null;
+  DistanceM: number | null;
+  ElevationM: number | null;
+}
+
 export interface ActivityListItem extends Activity {
   workout_kind_id: number | null;
   workout_kind_name: string | null;
@@ -128,6 +137,7 @@ export interface KindAssignment {
 export interface ReviewQueueItem extends KindAssignment {
   activity: Activity;
   laps: Lap[];
+  samples: Sample[];
 }
 
 export interface ProgressionPoint {