Port Bun concurrent-immediate reporter matrix

Track the next focused Bun compatibility tranche from #66.

Scope:

• run the byte-identical upstream js/bun/test/concurrent_immediate.test.ts corpus under Home
• retain the already-correct immediate concurrent hook ordering for sync and promise callbacks
• add Bun-compatible child-process banners and pass/fail reporter lines
• preserve error reporting parity between sync and promise fixtures
• 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 6965e52 (feat(test): port concurrent immediate reporter). The byte-identical upstream concurrent_immediate.test.ts now passes both sync/promise reporter assertions under Home. Existing immediate hook scheduling remains correct, while spawned runs now expose Bun-compatible version banners and pass/fail/error lines. The shared inline-snapshot reader was hardened for compact and multiline layouts; prior dots and done-callback exact corpora were revalidated. Final validation: exact corpus 2/2, focused regression, all five upstream byte comparisons, formatter/diff checks, and full home_test (1087 tests, 1 expected skip, 0 failures).