feat(system-builder): start from or look at a built-in example (4d1b)

[over2take]

From the approved builder-examples mockup. In + NEW, A BUILT-IN EXAMPLE is turned on: a card for CWN and Shadowrun each saying what it holds (health, advancement in the system's own XP word, stats, formulas, distance), and COPY makes a new draft under the name typed, opened on SETUP.

LOOK FIRST opens the example in the builder read-only: EXAMPLE · READ ONLY in the top bar, every page shown, SAVE and PUBLISH off. A Locked wrapper disables every control but those that only browse (tabs, open-out toggles, and buttons marked data-browse: the sheet designer's tree and the preview's viewers), and watches for more as pages draw. TRY IT stays usable, without SAVE AS THE SAMPLE CHARACTER. A banner offers COPY TO CHANGE IT and BACK TO + NEW. edit() refuses on an example as a second guard.

Summary

Test plan

• Tested locally
• Tests pass

Pre-merge checklist

Code quality:

• Code follows project style
• No breaking changes (or clearly documented)
• No console errors or warnings

Version & Release:

• Version bumped? If releasing to users, update:
  • frontend/package.json version
  • docker-compose.yml APP_VERSION
  • CHANGELOG.md with release notes
• GitHub Actions will auto-tag Docker images with the new version

Before merging to main:

• All tests passing
• PR reviewed and approved
• Branch is up to date with main
• No merge conflicts

Related issues