test(sync): increase coverage to 70% for statements and lines

- Add comprehensive tests for sync module components:
  - crossPlatformSync.spec.ts: Cross-platform sync orchestrator tests
  - syncLogManager.spec.ts: Sync log manager tests
  - syncManager.spec.ts: Sync manager tests
  - httpTransport.spec.ts: HTTP transport tests
  - websocketTransport.spec.ts: WebSocket transport tests
  - deviceManager.spec.ts: Device manager tests
  - conflictResolver.spec.ts: Conflict resolver tests
  - vectorClock.spec.ts: Vector clock tests
  - messages.spec.ts: Protocol messages tests
  - transport.spec.ts: Base transport tests

- Update vitest.config.ts:
  - Exclude electron adapters from coverage (requires native bindings)
  - Increase coverage thresholds to 70% for all metrics

Coverage results:
- Statements: 83.01% (was ~48%)
- Branches: 77.45% (was ~70%)
- Functions: 71.71% (was ~55%)
- Lines: 83.01% (was ~48%)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: 2 people