Add schema handling in Topic Panel

[bburda]

Summary

The topic endpoint now returns a message schema including field types. The Topic Panel must parse this schema and generate matching UI controls automatically. When the user changes values in the panel and sends a message, the UI must build a valid JSON payload that matches the schema.

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Proposed solution (optional)

1. Fetch schema metadata from the topic endpoint response.
2. Parse schema into a UI model (fields, types, optionality/defaults if available).
3. Render dynamic controls in the Topic Panel based on field types.
4. Build and send JSON that conforms to the schema.