docs: add branch strategy to CLAUDE.md

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

CLAUDE.md

@@ -1,5 +1,11 @@
 # pad_scanner CLAUDE.md
 
+## Branch Strategy
+
+- The main branch is `master`, always kept in a releasable state
+- All new feature development must be done on a `dev` branch, created from `master`
+- After verification, merge `dev` back into `master`
+
 ## App Installation Rules
 
 **Always use `adb install -r` to install the app. Never use `flutter install`.**