fix: typecheck hook false positives, add 11 session-manager tests
- Fix post-edit-typecheck.js error filtering: use relative/absolute path
matching instead of basename, preventing false positives when multiple
files share the same name (e.g., src/utils.ts vs tests/utils.ts)
- Add writeSessionContent tests (create, overwrite, invalid path)
- Add appendSessionContent test (append to existing file)
- Add deleteSession tests (delete existing, non-existent)
- Add sessionExists tests (file, non-existent, directory)
- Add getSessionStats empty content edge case
- Add post-edit-typecheck stdout passthrough test
- Total: 391 → 402 tests, all passing
3f651b7c3c