fix(studio): preserve zero caption scale

[tianma-if]

Summary

• preserve valid zero-valued GSAP caption transforms
• share finite-number fallback handling between the overlay and property panel
• add regression coverage for zero scale and non-finite values

Why

Both caption editing paths used value || 1 for scale. A caption intentionally animated to scale zero was therefore read back as scale one, causing editor interactions to make it visible again.

Validation

• bunx oxfmt and bunx oxlint on changed files
• bun run --filter @hyperframes/studio test -- CaptionOverlayUtils.test.ts
• bun run --filter @hyperframes/studio typecheck