Add the core explicit icon catalog

[konojunya]

Summary

• add 12 provider-neutral, repository-authored explicit icons to all three core themes
• allow themes to share an SVG only when its logical ID and complete asset metadata match
• release the catalog source and generated Cargo/npm artifacts as version 0.2.0
• extend the review gallery and record desktop/mobile visual evidence

Verification

• npm ci
• npm run validate
• npm run generate:check
• npm test
• npm run typecheck
• npm pack --dry-run --workspace @stack-sh/theme
• cargo +stable fmt --check
• cargo +stable test --workspace --locked
• cargo +stable clippy --workspace --all-targets --locked -- -D warnings
• RUSTDOCFLAGS=-D warnings cargo +stable doc --workspace --no-deps --locked
• cargo +stable package -p stack-theme --locked
• isolated headless Chrome at 1440x1000 and 390x844: 36 explicit icon cards, no overflow, console/page/network errors empty