Activate Bun pretty-format overflow regression

Track the next focused Bun compatibility tranche from #66.

Scope:

• activate the byte-identical upstream js/bun/test/pretty-format-overflow.test.ts corpus under Home
• verify deeply nested mismatch formatting exits as a normal test failure without panic, integer overflow, or SIGTRAP
• retain the expected expect(received).toEqual(expected) diagnostic
• add permanent Home regression coverage and run the full home_test gate

Baseline after removing the stale native-TODO gate is already 1/1 passing; this issue records and protects that capability.

Completed in ded0c3a (test: activate pretty format overflow corpus). The stale native-TODO gate is removed and the byte-identical upstream pretty-format-overflow.test.ts now runs permanently under Home. Its 500-level nested mismatch exits normally with the expected expect(received).toEqual(expected) diagnostic and without panic, integer overflow, or SIGTRAP. Validation passed: exact corpus 1/1, focused regression, upstream byte comparison, formatter/diff checks, and full home_test (1088 tests, 1 expected skip, 0 failures).