Add Flow conditions for speaker state

[jelledelaender]

Goal

Expose useful SoundTouch state as Homey Flow conditions.

Candidate Conditions

• Speaker is playing.
• Current preset is a selected preset number.
• Speaker is available/reachable.
• Current source equals a selected/source value, if source state is reliable enough.

Context

The app already tracks playback state, active preset, source, and availability internally. Flow conditions would let users branch automations based on the speaker state.

Acceptance Criteria

• Flow condition cards are available for the SoundTouch driver.
• Conditions use current device state without triggering playback.
• Missing/unknown state returns a conservative false result.
• npx homey app validate passes.