Add runtime atlas follow-up polish

[agustin-littlehat]

Summary

• bake the main menu presentation assets and menu styling
• update pointer/mobile controls and orientation handling
• improve runtime atlas visibility, CSS image rendering, and deterministic atlas behavior

Validation

• pnpm build in detached temp worktree at 4449485
• git diff --check origin/main..HEAD

Note: this PR contains only the already committed branch history. The local uncommitted src/runtime/shootables.ts change was not included.