Add protocol-neutral language intelligence - #11

Summary

• add stateless native APIs for versioned diagnostics, context-aware completion, semantic hover, and hierarchical document symbols
• validate source positions and bounded caller-owned icon catalogs without adding runtime dependencies
• adopt the canonical language-intelligence 1.0 fixtures from specification revision 0545936ecaebe77b9309bacd0447b8073a1d0701
• document compiler, formatter, and protocol-adapter ownership boundaries
• cross-build the same semantic core for wasm32-unknown-unknown in CI

Verification

• cargo fmt --check
• cargo test
• STACK_SPECIFICATION_DIR=../specification cargo test --features conformance --test conformance --test language_intelligence_conformance
• cargo build --lib --target wasm32-unknown-unknown --locked
• cargo clippy --all-targets --all-features -- -D warnings
• RUSTDOCFLAGS=-Dwarnings cargo doc --no-deps
• cargo llvm-cov --lib --all-features --workspace --fail-under-lines 95 --fail-under-functions 95 --fail-under-regions 95
• cargo publish --dry-run --locked