test: add Phase 3 tests (multi-root workspace + permalinks)

Phase 3 - Workspace & Navigation (#98):
- multiRoot.test.ts: 35 tests for workspace root management,
  unique label generation, and path resolution
- permalinks.test.ts: 44 tests for GitHub/GitLab/Bitbucket
  permalink generation, SSH URL handling, and line formatting
- navigation.test.ts: 32 tests for partially audited region
  navigation, wrapping, and multi-root traversal

Total: 398 tests passing

Closes #98

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Co-Authored-By: Claude <[email protected]>

Author: fegge