Bun parity: implement AbortSignal.any composition semantics

Scope

Port Bun's js/web/abort/abort.test.ts at corpus position 4086 by implementing AbortSignal.any() in the Home Bun-compat bootstrap.

Acceptance criteria

• aborts when either input signal aborts and preserves the winning reason
• handles already-aborted inputs deterministically
• removes listeners from losing signals after settlement
• rejects malformed iterables/signals with a structured ERR_ABORT_SIGNAL_ANY error
• diagnostic includes operation, input index, cause, and a composed operation stack
• focused Bun corpus file passes with zero failures/unsupported tests
• permanent regression coverage is added

Tracked from #66.

Implemented and pushed to main in 762822749 (feat(abort): port signal composition semantics).

The Home Bun-compat bootstrap now provides AbortSignal.any() with:

• first-abort propagation and exact winning-reason identity
• deterministic already-aborted input handling
• cleanup of listeners attached to losing signals
• iterable and signal validation
• structured ERR_ABORT_SIGNAL_ANY failures carrying operation = abort.signal.any, inputIndex, the original cause, and a composed operation/cause stack

Permanent regression coverage checks the upstream file, structured invalid-input diagnostics, already-aborted reasons, and losing-listener cleanup.

Verification:

• focused js/web/abort/abort.test.ts: 5 passed, 0 failed, 0 todo, 0 unsupported
• positions 4084–4086 together: 3 files, 12 passed, 0 failed, 0 todo, 0 unsupported, 0 allowed-empty
• permanent gRPC error-stack suite: passed
• permanent SQL adapter contracts: passed
• permanent third-party/error-diagnostic suite: passed (51 diagnostic cases)

This completes the acceptance criteria. Parent tracker: #66.