Migrate tests to use insta snapshot testing
Changes:
- Fix Cargo.toml dev-dependencies typo (dev.dependencies → dev-dependencies)
- Add insta with yaml features for snapshot testing
- Convert all 21 tests from assert_eq! to assert_snapshot!
- Generate snapshot files for all test cases
Benefits:
- Much easier to review and update test expectations
- Better diff output when tests fail
- Can use `cargo insta review` to update snapshots
- Snapshots capture the actual rendered output format
All 21 tests passing with new snapshot approach.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
