feat: type-safe .riv schema system

[mfazekas]

Supersedes #294 (same feature, re-based onto main after the experimental-runtime merge in #134; squashed there since every commit conflicted with the runtime rewrite).

Codegen pipeline that extracts artboard/state machine/ViewModel schemas from .riv files and surfaces them as TypeScript phantom types — no runtime overhead. yarn rive-gen-types example/assets/rive/rewards.riv (or --all) emits a .riv.d.ts next to each asset; importing the asset then constrains artboardName/stateMachineName, viewModelName, property paths per kind, and enum value unions across RiveView, useRiveFile, useViewModelInstance, and the useRive* property hooks. See #294 for the full API walkthrough.

Changes relative to #294:

1. Merged with the experimental-runtime changes: RiveFileFactory keeps getBackend(), the loadCdn deprecation warning and optional loadCdn? signatures, now with the typed generics on top; RiveView keeps the new docs/frameRate while its props are generic over the schema.
2. Bumped @rive-app/canvas to 2.39.0 and regenerated all schemas — output is byte-identical, so the extractor works with the new runtime as is.
3. Generated schemas for assets added on main since the branch (tabtest.riv, arbtboards-models-instances.riv).

Note: rive-wasm 2.39.0 now exposes ViewModelProperty.enumName, so the "enum names not accessible" limitation from #294 is gone — a follow-up can emit named enum types instead of inlined value unions.