fix(ui): toggle stays clickable during battery suspend — D-138 player autonomy

Player autonomy wins: AI Dialogue toggle is only greyed out for RAM fail
(< 1.6 GB free). Battery suspend shows a warning label instead of
disabling the toggle — player can override the auto-suspend at any time.

Changes:
- settings_dialog: toggle disabled = hw_status == "fail" only
- settings_dialog: add _ai_battery_warning_label (STATUS_YELLOW) shown
  when _ai_inference_suspended; hidden when plugged back in via
  set_ai_inference_suspended()
- settings_dialog: is_ai_dialogue_toggle_enabled() no longer checks
  _ai_inference_suspended
- settings_dialog: set_ai_inference_suspended() updates warning label
  visibility, not toggle disabled state
- ui-strings: add settings.ai_battery_warning "High battery usage"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/data/ui-strings.yaml

@@ -199,6 +199,7 @@ settings:
   ai_dialogue_toggle: "AI-Enhanced Dialogue"
   ai_status_checking: "Speed not yet measured — will check on first enable."
   ai_status_ram_marginal: "Low memory — performance may vary."
+  ai_battery_warning: "High battery usage"
 
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