test: add regression coverage for frame and animation APIs

[ubugeeei]

Finding

The core frame/animation APIs have no automated tests, despite being the basis for deterministic rendering.

Evidence

• No .test. or .spec. files exist in the repository.
• src/lib/frame.tsx and src/lib/animation.ts mutate shared frame state and window.__frameScript hooks.

Acceptance criteria

• Add a test runner appropriate for the repo.
• Cover frame setters/getters, seconds conversion, animation variable compatibility, and deterministic frame progression.
• Add the test script to CI after it is stable.

[ubugeeei]

対応済みです。修正は PR #1 / commit 9cf4498 に反映済みです。