Add a permanent public coworking lobby on the ground floor

[schnepg1]

Change

Adds a permanent shared coworking lobby on the ground floor (G). Everyone arrives there, including when the building has no project floors. Project floors start at 1; the elevator and floor list keep the lobby available after the last project is removed.

The lobby has human seating and shared social amenities, with drawings and music persisted in the building data directory. Worker hiring, project files and project controls remain scoped to project floors. Includes documentation and lobby/server dispatch tests.

Based on upstream main at 7f7211e, with the current model catalogue and README changes preserved during integration. This PR contains only the public lobby contribution; the Windows Codex hooks and floor capacity changes are separate.

Validation

• Windows, Node 24.12.0: typecheck and production build pass.
• All 14 focused lobby, server dispatch and source size tests pass on this branch.
• Combined local integration: all 22 focused lobby, Codex, server dispatch and size tests pass.
• npm run dev starts both Vite and the office server with the already merged Windows startup fix (npm run dev opens the office on Windows instead of hanging before it listens #224).
• Headless Chromium: sign in, character selection, public lobby arrival with no projects, and elevator listing G were checked; screenshots captured locally. 3D rendering triggers the slow-computer warning in this environment.
• The full Windows test suite reports two client registry failures and six building clone failures; the same named failures occur on unchanged upstream 7f7211e. Full-suite runs did not finish and were stopped, including a repeat with a 60-second test timeout. This is not a full-suite pass.

Draft pending the contributor's interactive playthrough and CI/review. No preceding issue was opened.