feat(system-builder): the STATS & RULES page as logic (4b2c)

[over2take]

sheets/statsRules.ts: stat groups and stats (withNewGroup / withGroupLabel / withoutGroup, withNewStat / withStat / withoutStat, with ranges and ties), the sample character (sampleOf / withSample), formulas (withNewFormula / withFormula / withoutFormula, usedBy, problemsByFormula, insertToken), tables (withNewTable / withTableLabel / withoutTable, withBands, lookupIn). Ids come from first names via setup.idFor and never take one already used (takenIds: the starter sheet's and health section's fields, groups, stats, formulas, tables, the engine's functions). Removing a stat takes its sample and ties to it; empty sections are removed.

systemsApi gains previewValues (POST /api/systems/preview-values).

Held to the server: every step passes definition.js's check, the built system works out through derived.previewDerived, FUNCTIONS matches expression.js BUILTINS. Approved mockup builder-stats-rules, 2026-10-06.

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