feat: the graph view's layout can be saved (5a1)

[over2take]

A system can hold the map's layout in a new graph section: positions, groups of formulas, folded groups and notes. No wires: they are the formulas. Checked as strictly as the rest of an untrusted file (shape, counts, ids), but nothing done in FORMS can make a problem in it: a leftover naming something deleted is left out by the map. Carried in a .citysys file, never in what players get. The FORMS / GRAPH choice for STATS & RULES is remembered on the server, main admin only.

The random-system generator now makes layouts too, so the soak and hostile-file tests cover them.

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