Port Bun new snapshot file workflow

Track the next focused Bun compatibility tranche from #66.

Scope:

• run the byte-identical upstream js/bun/test/snapshot-tests/new-snapshot.test.ts corpus under Home
• create __snapshots__/new-snapshot.test.ts.snap when both the directory and file are absent
• recreate the snapshot when the file is removed but the directory remains
• preserve successful child test exit behavior with CI=false
• add permanent Home regression coverage and run the full home_test gate

This issue will be closed by the direct-main implementation commit.

Completed in 4eacbdf (feat(test): port new snapshot workflow). The byte-identical upstream new-snapshot.test.ts now passes under Home. Spawned tests create __snapshots__/new-snapshot.test.ts.snap when both directory and file are missing, then recreate it after file deletion while retaining the directory, with successful CI=false exits. Permanent aggregate coverage was added. Validation passed: exact corpus 1/1, focused regression, both upstream byte comparisons, formatter/diff checks, and full home_test (1093 tests, 1 expected skip, 0 failures).