Integrate the core icon catalog

[konojunya]

Summary

• pin the final Stack Theme 0.2.0 revision and update Engine and browser package versions to 0.3.0
• verify all 12 provider-neutral icon identifiers and subjects across every core theme
• add an explicit api icon fixture shared by native and browser operations with a byte-stable standalone SVG snapshot
• preserve missing-icon fallback diagnostics while updating package documentation and dependency evidence

Validation

• cargo +stable fmt --check
• cargo +stable test --workspace --locked
• canonical formatter and Engine conformance suites against specification 7f9154d22702ddf02f2713bbc06dde7bdf635806
• python3 scripts/validate-svg.py
• npm run build:wasm
• npm test
• npm run typecheck
• npm run pack:check
• WASI numeric parity with Wasmtime 48.0.1
• cargo +stable clippy --workspace --all-targets --all-features --locked -- -D warnings
• RUSTDOCFLAGS="-D warnings" cargo +stable doc --workspace --no-deps --locked
• cargo +stable llvm-cov (97.25% lines, 97.13% functions, 95.50% regions)
• Rust 1.85 workspace tests and Clippy
• clean consumer install and render smoke test for all 12 explicit icons