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/sprite-pipeline.md

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+# Sprite Pipeline
+
+This is the default 2D animation workflow for the plugin.
+
+## Principles
+
+- Start from one approved in-game frame.
+- Generate the animation as one strip, not isolated frames.
+- Normalize the whole strip with one shared scale.
+- Use one shared anchor, typically bottom-center.
+- Preview before approving the asset.
+
+## Why this works
+
+- The approved seed frame preserves identity.
+- Strip-first generation reduces frame-to-frame drift.
+- Shared-scale normalization prevents one tall pose from making the character feel smaller.
+- Locking frame 01 back to the shipped sprite preserves continuity for idle-to-action transitions.
+
+## Prompt template
+
+```text
+Intended use: candidate production spritesheet for a 2D browser game animation review.
+Edit the provided transparent reference canvas into a single horizontal <N>-frame spritesheet.
+
+The existing sprite in the leftmost slot is the anchor frame and must remain the same character:
+- same facing direction
+- same silhouette family
+- same palette family
+- same proportions
+- same readable face or key features
+- same outfit details
+
+Composition:
+- transparent canvas
+- exactly one row of <N> equal frame slots
+- no extra characters
+- no labels
+- no scenery
+- no poster layout
+
+Action:
+- describe the specific animation beat from frame 1 through frame N
+
+Style:
+- authentic pixel-art production asset
+- crisp pixel clusters
+- restrained palette
+- not concept art
+```
+
+## Normalization notes
+
+- Use the union of detected sprite bounds per slot.
+- Compute one scale from the largest detected frame and anchor.
+- Bottom-align frames into the target canvas.
+- Reuse the exact shipped frame for frame 01 when `--lock-frame1` is appropriate.