fix: updated readme

[gitsad]

What does this PR do?

Brings the @mobile-reality/mdma-agui README in line with the bridge it ships. It still described
the 0.2.x surface, so 0.3.0 published with docs that were wrong in places — and a sentence left
truncated mid-phrase by a stale link removal.

Type of Change

• Bug fix (non-breaking change that fixes an issue) — docs were factually wrong
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing behavior to change)
• Refactor (no functional change)
• Documentation
• CI / tooling

Packages Affected

• @mobile-reality/mdma-agui
• @mobile-reality/mdma-spec
• @mobile-reality/mdma-parser
• @mobile-reality/mdma-runtime
• @mobile-reality/mdma-attachables-core
• @mobile-reality/mdma-renderer-react
• @mobile-reality/mdma-prompt-pack
• Blueprint: ___________

Checklist

• I have read the CONTRIBUTING guide.
• My code follows the existing code style (pnpm format and pnpm lint pass).
• I have added or updated tests that cover my changes — n/a, docs only.
• All tests pass (pnpm test).
• Type-checking passes (pnpm typecheck).
• I have added a changeset — patch → mdma-agui 0.3.0 → 0.3.1.
• New or changed MDMA schemas are backwards-compatible — n/a.
• Sensitive fields are marked with sensitive: true — n/a.