feat(runtime): feature parity checklist automated tests

[viniciusdacal]

Description

Systematically verify every row in the Feature Parity Checklist from the original runtime plan. Write automated integration tests that run against both Bun and Rust dev servers verifying identical behavior. See plans/vertz-dev-server/next-steps.md Section 3.3.

Key files: native/vertz-runtime/tests/parity/ (new directory) — tests per feature area: http_serving.rs, static_files.rs, compilation.rs, ssr.rs, hmr.rs, error_overlay.rs, diagnostics.rs

Estimated effort: L (2-3 weeks)

Acceptance Criteria

• Every "Included" row in parity checklist has at least one automated test
• Tests run as part of cargo test --test parity
• "Deferred" features documented as explicitly not tested with reference to plan
• Summary report maps each checklist row to test file and status

[viniciusdacal]

#2077 added API delegation, SSR reuse, fetch interception, and server module hot-swap — these need parity test coverage added to the matrix.