Fix sleep score parsing, dashboard body battery, segment direction

- Garmin sync: read sleepScores from dailySleepDTO (Garmin nests it there),
  so sleep score is actually stored instead of always null
- Dashboard: pass YYYY-MM-DD to the intraday endpoint (was a full ISO
  timestamp), so the body-battery tile populates
- Segment matching: follow the segment in its created direction with a
  path-length sanity check, so out-and-back routes no longer match an early
  start pass to a late finish (the >1h bogus segment times)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/pages/DashboardPage.jsx

@@ -152,7 +152,7 @@ export default function DashboardPage() {
     const rows = [...(recentHealth || [])].sort((a, b) => new Date(b.date) - new Date(a.date))
     const pick = f => rows.find(d => d[f] != null)?.[f] ?? null
     return {
-      date: rows[0]?.date ?? null,
+      date: rows[0]?.date ? rows[0].date.slice(0, 10) : null,   // intraday endpoint wants YYYY-MM-DD
       resting_hr: pick('resting_hr'),
       sleep_duration_s: pick('sleep_duration_s'),
       hrv_nightly_avg: pick('hrv_nightly_avg'),