[codex] add sprite studio tooling

[osdeving]

Summary

• Add the external Tauri + React Sprite Studio under tools/sprite-studio.
• Document the Sprite Studio workflow, architecture decision, and sprite/combat metadata contracts.
• Improve the desktop UI chrome, toolbar, timeline, frame combat summary, and in-app help/tutorial.

Why

Artists and gameplay tuning need a desktop workflow for inspecting sprite manifests, adjusting scale/pivot/combat boxes, validating runtime assets, and exporting review artifacts without depending on the Raylib game loop.

Validation

• git diff --check
• cd tools/sprite-studio && pnpm build
• cargo test --test sprite_manifest
• Manual Vite/Playwright visual check of the Sprite Studio help and UI chrome

[sourcery-ai]

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