landing: update for Z3 backend, KRaft spec, remove WAT WASM generator
- Replace WASM pipeline artifact with Z3 Verification (SMT-LIB2)
- Add Kafka KRaft as flagship example (141 lines, 6 invariants)
- Add Status & Roadmap section (TS codegen ✅, Z3 ✅, OAuth2 ✅, Rust 🚧, WASM 📋)
- Remove WAT/WASM quickstart commands; add --target=z3 example
- Update example count to 14, include OAuth2AuthorizationCode and PreconditionTest
- Remove remaining WASM/WAT references in meta tags, comments, copy
- Keep "Don't replace Kafka. Prove it." positioning