Extend rust-development with FFI and cross-language integration section

[AlexMikhalev]

Parent Epic: #62

What

Add FFI and cross-language integration patterns to rust-development SKILL.md.

Sections to Add

1. Safe C API Wrappers -- Opaque handle pattern, #[repr(C)] structs, extern "C" functions
2. Panic Catching at FFI Boundary -- std::panic::catch_unwind at every extern entry point
3. String Management Across Languages -- CString/CStr patterns, null-terminated strings, ownership transfer
4. uniffi for Automatic Bindings -- Generating Kotlin/Swift/Python bindings from Rust
5. WASM Interop Patterns -- wasm-bindgen, js-sys, shared memory, serde-wasm-bindgen

Source Reference

Section 10 (FFI and Cross-Language Integration) from RUST_SYSTEM_PROGRAMMING_BEST_PRACTICES.md

Disciplined Engineering Alignment

Phase	Skill	FFI Relevance
Research	disciplined-research	Map FFI boundary surface area; identify which language bindings needed; catalogue existing unsafe FFI
Design	disciplined-design	Define opaque handle API; specify ownership transfer rules; document WASM vs native FFI strategy
Implementation	disciplined-implementation	Each FFI function = one step with safety invariants documented; panic-catch wrappers first, then logic
Verification	disciplined-verification	Miri on unsafe FFI paths; property tests for string conversion roundtrips; fuzz parsers at boundary
Validation	disciplined-validation	Validate bindings from target language (Kotlin/Swift/JS); end-to-end cross-language integration test

The SKILL.md should note:

• During research: audit all extern blocks and unsafe FFI for safety gaps
• During design: specify ownership transfer semantics at every FFI boundary
• During verification: Miri + fuzzing mandatory for any new FFI surface

Acceptance Criteria

• SKILL.md updated with FFI section including code examples
• WASM-specific patterns included (not just C FFI)
• Unsafe code policy section cross-referenced
• Disciplined workflow integration notes included