Task 1d — Add config option for low-confidence threshold and feedback phrase

Task 1d — Make low-confidence threshold and phrase configurable

Part of Task 1: Low Confidence Voice Feedback. Depends on #374 (Task 1b) and #375 (Task 1c).

What to do

Once TTS and visual feedback are working (Tasks 1b and 1c), expose the key values as user-configurable settings.

• Add low_confidence_threshold (float, default matching current hardcoded value) to config.json / settings schema.
• Add low_confidence_phrase (string, default "I didn't quite catch that") to config.
• Read both values at runtime in the relevant handlers so users can tweak sensitivity and the spoken phrase without touching code.

Files to touch

• Config schema / config.json defaults
• Handler introduced in Task 1b (read phrase from config)
• Listener threshold check in Task 1a (read threshold from config)

Acceptance criteria

• low_confidence_threshold is read from config (falls back to current default if absent)
• low_confidence_phrase is read from config (falls back to "I didn't quite catch that" if absent)
• Changing these values in config takes effect on next Jarvis start
• Documented in config schema or README