fix(npm): fall back after prebuilt SIGILL

[snvtac]

Summary

• let the npm wrapper continue to the bundled Bun runtime when an auto-discovered native prebuilt exits with SIGILL
• preserve normal native exit codes and keep HUNK_BIN_PATH override failures non-fallback
• add wrapper regression coverage and a patch changeset for hunkdiff

Fixes #454.

Validation

• bun test test/cli/entrypoint.test.ts --test-name-pattern "bin wrapper"
• bun test test/cli/entrypoint.test.ts
• bun run typecheck
• bun run format:check
• bun run lint
• git diff --check
• bun run build:npm
• bun run check:pack
• bun run changeset:status
• bun run test
• bun run build:prebuilt:npm
• bun run check:prebuilt-pack
• bun run smoke:prebuilt-install
• bun run test:integration
• bun run test:tty-smoke

Notes

• I could not run the original Docker/QEMU repro locally because the Docker CLI is not available in this environment.

[greptile-apps]

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