Initial release: game-studio plugin for Claude Code

Repackaged from OpenAI's game-studio Codex plugin (MIT) for Claude Code.

Changes from upstream:
- Added .claude-plugin/plugin.json (Claude Code plugin manifest)
- Removed .codex-plugin/plugin.json (Codex CLI specific)
- Removed skills/*/agents/openai.yaml (Codex CLI specific)
- Added scripts/requirements.txt (Pillow dependency for sprite-pipeline)
- Added Chinese README with installation guide

references/playtest-checklist.md

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+# Playtest Checklist
+
+Use this checklist for browser-game QA.
+
+## Universal checks
+
+- Does the game boot into a useful first state?
+- Are the main verbs obvious and responsive?
+- Does the HUD remain readable over gameplay?
+- Does the first playable screen prioritize play over dashboard chrome?
+- Does the central playfield stay mostly clear during normal play?
+- Do pause, failure, and recovery states work?
+- Does the game survive viewport changes?
+
+## 2D checks
+
+- sprite baseline consistency
+- hit, hurt, and attack timing
+- command menu focus and input state
+- tile or platform readability
+- particle or camera effects obscuring gameplay
+
+## 3D checks
+
+- camera control stability
+- camera and menu-state handoff
+- depth readability
+- persistent overlay weight versus scene readability
+- secondary notes, controls, and quest details collapsed by default
+- resize and aspect-ratio handling
+- renderer fallback or context-loss handling
+- material and lighting stability across states
+- GLB asset and texture streaming behavior
+- collision proxy alignment
+- GPU bottlenecks isolated with capture tools when needed
+
+## Browser checks
+
+- desktop and mobile viewports
+- input modality differences
+- reduced-motion behavior
+- pause behavior when focus changes
+- pointer-lock and camera-input release when overlays open
+- transient onboarding hints dismiss or fade once the player is moving
+
+## Reporting
+
+- Capture screenshots for visual findings.
+- Put findings in severity order.
+- Include reproduction steps.
+- Call out whether the likely owner is simulation, renderer, frontend, or asset pipeline.