feat(system-builder): MY SYSTEMS in the builder; SYSTEMS.EXE retired …

[over2take]

…(4a2c2b)

The builder's MY SYSTEMS page is MySystemsPage: OPEN saves the open system first, then opens the other here (onOpenSystem(id, page)); its messages go to the builder's status line. The builder opens with no system (systemId null): MY SYSTEMS only, the other pages and SAVE / PUBLISH off, NO SYSTEM OPEN in the top bar, nothing fetched but the list.

The GAME tab's button is SYSTEM BUILDER and opens the builder on MY SYSTEMS, with the running system open when it is a custom one. The SYSTEMS.EXE window (components/SystemsWindow.tsx) and its tests are removed; its GAME-tab tests move to BuilderScreen.test.tsx. Approved mockup builder-my-systems, 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

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