[feature request] Speech option: enable only when armed

Text to speech is very useful, but it can get a bit much when disarmed.

Search the Mission Planner codebase for the text-to-speech implementation and the handling of armed versus disarmed vehicle state. Determine where the speech option is configured and how state changes are exposed. Done means speech can be enabled for armed vehicles while remaining disabled when disarmed, with the behavior verified in the relevant application flow.

Written by the indexing model from the issue text.