docs: mark deprecated API entries

[mikaello]

Summary

• render a Deprecated badge and highlighted migration notice from rescript-tools metadata
• include deprecation messages in API filtering without parsing docstrings
• preserve the mobile layout when badges wrap

Testing

• npm run docs:build
• npm run check
• npm test (220 tests)
• browser check at 390px width
• verified filtering for deprecated returns 45 badged entries and no horizontal overflow