Fitbit Air: Health Connect sync + vitals dashboard

- react-native-health-connect (config plugin, minSdk 26, 11 read perms)
- sync-on-open + manual sync: incremental via server watermark, chunked
  POST to /api/health/v1/fitbit/sync (HR, resting HR, HRV, SpO2, resp
  rate, steps/distance/kcal/floors dailies, staged sleep sessions)
- Fitbit screen: steps/RHR/HRV/SpO2 tiles + daily charts + sleep list +
  per-stream record counts (answers the which-types-does-Google-Health-
  share question empirically)
- Sleep tab now merges Fitbit Air nights (wins over older sources)
- Today screen Fitbit card

Server side (deployed separately on VPS): hc_samples/hc_daily/hc_sleep
tables + sync/latest/summary endpoints in health-api; Caddy routes POST
/api/health/v1/fitbit/* behind the same basic_auth.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app.json

@@ -15,6 +15,19 @@
     },
     "android": {
       "package": "xyz.rehbock.health",
+      "permissions": [
+        "android.permission.health.READ_HEART_RATE",
+        "android.permission.health.READ_RESTING_HEART_RATE",
+        "android.permission.health.READ_HEART_RATE_VARIABILITY",
+        "android.permission.health.READ_OXYGEN_SATURATION",
+        "android.permission.health.READ_SLEEP",
+        "android.permission.health.READ_STEPS",
+        "android.permission.health.READ_RESPIRATORY_RATE",
+        "android.permission.health.READ_DISTANCE",
+        "android.permission.health.READ_ACTIVE_CALORIES_BURNED",
+        "android.permission.health.READ_TOTAL_CALORIES_BURNED",
+        "android.permission.health.READ_FLOORS_CLIMBED"
+      ],
       "adaptiveIcon": {
         "backgroundColor": "#0d0d0f",
         "foregroundImage": "./assets/images/android-icon-foreground.png",
@@ -30,6 +43,15 @@
     "plugins": [
       "expo-router",
       "expo-secure-store",
+      "react-native-health-connect",
+      [
+        "expo-build-properties",
+        {
+          "android": {
+            "minSdkVersion": 26
+          }
+        }
+      ],
       "./plugins/with-release-signing.js",
       [
         "expo-splash-screen",