v1.0.31: fix remaining sync loop triggers + icon redesign

Three additional fixes found via live device logs:

1. Startup race window: FileObserver fires immediately after
   startWatching() before catchupScan coroutine runs, starting a 5s
   debounce with cooldown=0. Fixed by setting a 15s startup cooldown
   in watchPath() BEFORE calling watchDirRecursive.

2. Stale debounce bypass: debounce job started with cooldown=0 fires
   5s later even after catchupScan has already set cooldown and started
   a catchup sync. Fixed by re-checking cooldown after the 5s delay
   and aborting if already active.

3. Debounce not cancelled by catchupScan: if a debounce was queued
   before catchupScan ran, catchupScan would enqueue a catchup sync
   AND the old debounce would fire 5s later enqueuing a second sync.
   Fixed by cancelling pending debounce in catchupScan before enqueue.

Icon: four thick arcs (blue/red/green/orange) in a 4-way pinwheel
with over/under ordering. White sync-arrow circle at center.
Pure black background.

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

version.properties

@@ -1,2 +1,2 @@
-VERSION_NAME=1.0.30
-VERSION_CODE=31
+VERSION_NAME=1.0.31
+VERSION_CODE=32