fix(studio): make optional file reads explicit

[func25]

What

Make optional file reads explicit in the Studio file API.

Why

Studio still has a compatibility read for .hyperframes/studio-motion.json. That read is optional, but the file route treated it like a normal required file. This caused 404 console noise when the file was missing.

How

Let callers mark optional reads with optional=1. When that flag is set, missing files return empty content. Normal file reads still return 404 for missing files.

Test plan

How was this tested?

• Unit tests added/updated
• Manual testing performed
• Documentation updated (if applicable)