Implement onGetAvailableForms handler

[najuna-brian]

Closes #70

Summary

Implements the onGetAvailableForms handler to return actual form data instead of an empty array, enabling custom apps to discover available forms programmatically.

Changes

• FormulusMessageHandlers.ts: Implemented onGetAvailableForms to query FormService and transform FormSpec[] to FormInfo[]
• FormulusMessageHandlers.types.ts: Updated return type from Promise<any> to Promise<FormInfo[]>

Testing

• Custom apps can now call await formulus.getAvailableForms() and receive actual form data
• Returns proper FormInfo[] structure with all required fields
• Native screens unaffected (they use useForms() hook directly)

[r0ssing]

This is great! Thanks @najuna-brian - will you resolve the merge conflicts, so we can merge this into dev?