SpaceView cleanup: fix no-case-declarations, deps, prefer-const

[sugan0tech]

Summary
Clean up SpaceView to satisfy lint rules and avoid subtle bugs from stale closures and switch-case scoping.

Context
src/components/game/SpaceView.tsx has:

• no-case-declarations inside a switch.
• Missing dependencies in useEffect/useCallback (e.g., lines ~480, ~515, ~560 warnings).
• Unused refs/vars (usersRef, isMounted, offsetX/offsetY), and prefer-const hints.

Tasks

• Wrap case blocks or extract logic to functions to satisfy no-case-declarations.
• Fix hook dependency arrays by adding required deps or refactoring to stable callbacks/refs.
• Remove unused refs/vars; switch let to const where not reassigned.
• Smoke test interactions (rendering, input handling) to ensure parity.

Acceptance Criteria

• npm run lint passes for SpaceView without warnings/errors listed above.
• Manual sanity test shows movement/interaction still works as before.