fix: merge 4 mobileSyncConflict scenarios into 1 to fit CI budget, fix git process leaks and error handling

- Consolidate 4 separate mobileSyncConflict scenarios into a single scenario
  with 4 parts, saving 3 app restarts (~2min on CI)
- Add Observable teardown to kill git child processes on unsubscribe
- Propagate stdin errors to subscriber instead of silently logging
- Validate git service parameter against allowlist
- Reorder readOnly check before expensive git operations
- Add error event handler to all git child process spawns

.github/workflows/test.yml

@@ -52,7 +52,7 @@ jobs:
           # Set Chinese locale for i18n testing
           LANG: zh_CN.UTF-8
           LC_ALL: zh_CN.UTF-8
-        timeout-minutes: 25
+        timeout-minutes: 15
 
       # Upload test artifacts (screenshots, logs)
       - name: Upload test artifacts