feat(system-builder): SYSTEMS.EXE's NEW and INSTALL folders (4a1c2)

[over2take]

NEW: a name and CREATE (blank only; example and genre starts shown, off, for 4d1/4d3). A
taken name is refused in place, text kept and focused. Made: shown picked in SYSTEMS.

INSTALL: a .citysys file chosen or dropped (over 1 MB refused without sending), previewed as its cover, INSIDE badges, problems and installPlan's notices; its buttons install as offered, REPLACE asking first and only then sending replaceChanges, a blocked UPDATE saying why. Installed: the status line says what happened and the list has it; the picker is told.

The empty list now points to NEW and INSTALL.

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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