v1.0.16: spinning sync icon, colorful icon, ON_CHANGE fix, notification fix

- Sync icon now rotates (CSS-style spin) in StatusPill, StatusBanner,
  and card sync button whenever status is SYNCING
- Launcher icon redesigned: indigo→violet→cyan gradient background,
  upload arrow fades white→sky-blue, download arrow fades white→violet,
  soft glow ring behind arrows
- Fix ON_CHANGE not triggering: FileWatchService.start() now called
  from AddPairViewModel.save() so pairs created with ON_CHANGE
  immediately begin watching without needing a toggle or reboot
- Fix FileWatch notification hidden: IMPORTANCE_MIN → IMPORTANCE_LOW
  so the "Watching N folders" notification shows in the shade

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/src/main/res/drawable/ic_launcher_background.xml

@@ -3,6 +3,7 @@
     <gradient
         android:type="linear"
         android:angle="135"
-        android:startColor="#312E81"
-        android:endColor="#6366F1"/>
+        android:startColor="#4338CA"
+        android:centerColor="#7C3AED"
+        android:endColor="#0891B2"/>
 </shape>