test(compile): #678 add Ink linker smoke

[andrewtdiz]

Summary

Adds a real Ink compile/link fixture that locks issue #678's V8-fallback linker contract. The current Ink repro now links; executing the binary reaches a separate hasOwnProperty runtime interop gap, so this fixture intentionally stops at link-time proof.

Changes

• Adds tests/release/packages/ink-link-smoke pinned to react@18.3.1 and ink@5.2.1.
• Verifies Perry can compile/link the original Linker: unresolved _perry_fn_..._render for V8-fallback modules referenced from main #678 shape without unresolved perry_fn/perry_closure Ink symbols.
• Documents linker-only package fixtures in tests/release/packages/README.md.

Related issue

Closes #678

Test plan

• cargo build --release clean
• cargo test --workspace --exclude perry-ui-ios --exclude perry-ui-tvos --exclude perry-ui-watchos --exclude perry-ui-gtk4 --exclude perry-ui-android --exclude perry-ui-windows passes
• Added release package fixture under tests/release/packages/
• (if CLI / stdlib / runtime API changed) Updated docs/src/
• (if touching a platform UI backend) Built -p perry-ui-<backend> locally on that platform

Additional validation:

• PERRY_BIN="$PWD/target/release/perry" tests/release/packages/_harness.sh --filter ink-link-smoke
• target/release/perry compile test-files/test_issue_678_v8_fallback.ts -o ... + Node diff
• target/release/perry compile test-files/test_issue_678_reexport_default.ts -o ... + Node diff
• cargo fmt --all -- --check
• git diff --check

Screenshots / output

PASS ink-link-smoke

=== _harness summary ===
  passed: 1
  failed: 0
  skipped: 0

Checklist

• I have NOT bumped the workspace version or edited CLAUDE.md / CHANGELOG.md (maintainer handles these at merge)
• My commits follow the loose feat: / fix: / docs: / chore: prefix convention used in the log
• I've read CONTRIBUTING.md and agree to the Code of Conduct