Add focus visual indicator to Phaser games

Users can now see when a Phaser game has keyboard focus via a green
glow (box-shadow) around the game container. This resolves P1.5 from
the implementation plan, improving discoverability of keyboard controls.

- Add hasFocus state to track focus/blur events
- Apply green box-shadow (0 0 0 2px #00ff00) when focused
- Smooth 0.2s transition for visual polish

Fix keyboard focus race conditions for all games

Sync implementation plan to reflect v1.9.10 tag

Sync implementation plan version with git tag v1.9.9

Update implementation plan version to v1.9.8

Consolidate implementation plan to remove completed checklist items

Reduced plan from 1050+ lines to ~175 lines whilst preserving:
- Current status summary and E2E screenshot status
- P3 optional enhancement items
- Architecture notes and reference implementations
- Troubleshooting guidance

All P0/P1/P2 items remain complete - only optional enhancements remain.

Polished release - all P0/P1/P2 complete, Phaser games working

Plan cleanup - stale checklist items updated

Fix Phaser keyboard input and E2E navigation

- Fixed App.tsx preventDefault blocking Phaser keyboard events
- Added data-phaser-game attribute for proper event propagation
- Added auto-focus to PhaserGame container for immediate input
- Added data-testid to carousel buttons for E2E reliability
- Fixed E2E navigation to use exact title matching

Document Phaser test mock in infrastructure section

Added note about the Vitest mock for Phaser in src/test/setup.ts
which enables unit tests to run with Phaser game imports in jsdom
environment.