[codex] Add animation project scaffold

[jamesrochabrun]

Summary

Adds Animation as a first-class project kind alongside prototypes and slide decks.

• Adds animation project metadata, library filtering, icons, empty-state copy, and README docs.
• Creates an animation scaffold with a timeline engine at resources/animations.jsx and a neutral starter index.html scene.
• Vendors React, ReactDOM, and Babel into animation projects under resources/vendor/ so previews do not depend on CDN access.
• Updates Codex/Claude prompt and handoff guidance to use the selected design system when present, or a simple plain default when none is selected.
• Adds unit coverage for animation project creation, prompts, handoff context, sidebar behavior, and design-library palette mapping.

Validation

• swiftc -parse on edited Swift source/test files.
• git diff --check.
• xcodebuild build -scheme EaselChat-Package -destination 'platform=macOS' succeeded. Xcode still prints existing SwiftLint plugin noise for CodeEdit dependencies.
• xcodebuild test -scheme Easel -destination 'platform=macOS' -only-testing:EaselTests/DesignKindSymbolPaletteTests passed.
• swift test --package-path Packages/EaselChat --filter EaselProjectManagerTests.createAnimationWritesTimelineScaffold is blocked before reaching the test by the existing CodeEditSymbols Bundle.module SwiftPM issue.