Replace the single-screen first-run banner with a 3-slide flow built
on the ui_modal scaffold:
1. Welcome
2. How to play (drag-and-drop / double-click / right-click hints)
3. Keyboard shortcuts (8 rows mirroring help_plugin's canonical list)
Navigation: primary Next button (advances; final slide reads
"Start playing" and writes first_run_complete), secondary Back button
(slide >0), tertiary Skip on slide 0. Arrow / Enter / Esc keep
working as accelerators.
OnboardingSlideIndex resource persists across despawn/respawn so the
rebuild system always knows which slide to show next.
All colours, spacing, typography come from ui_theme tokens; no
literals in the new code.
cargo build / cargo clippy --workspace -- -D warnings / cargo test
--workspace all green (813 passed, 0 failed, 8 ignored).
funman300
18d7c121a3