docs(examples): add AssemblyScript guest

[lntutor]

Summary

• add a minimal AssemblyScript guest exporting run and importing only nx.host_log_v2
• pin AssemblyScript 0.28.8 and include an ABI/runtime smoke test for imports, exports, memory, and exact log output
• document build and nx run steps plus the managed-memory env.abort caveat
• build and test the example in the existing WASM examples CI job

Verification

• npm ci && npm run build && npm test in examples/guest_assemblyscript
• target/release/nx run examples/guest_assemblyscript/guest.wasm
• /Users/loi/.cargo/bin/cargo test --workspace -q
• /Users/loi/.cargo/bin/cargo fmt --all -- --check
• /Users/loi/.cargo/bin/cargo clippy --workspace --all-targets -- -D warnings
• git diff --check

Closes #50

[lntutor]

Current head dc386cd2a78181caa4de67f780e922f8666946c2 is mergeable and the visible CI surface on this exact SHA is fully green: cross-platform Check, Clippy, and Test jobs on Ubuntu, macOS, and Windows; Format; Build WASM Examples; CLI Multi-process Smoke; Benchmark Comparator Tests; Ubuntu Profiling Artifacts; Benchmark Regression Gate; and the aggregate CI Success check all completed successfully. There are no review threads or review-body comments open on the current PR state, so if this AssemblyScript guest example still matches the intended direction, it looks ready for maintainer review/merge when convenient.