feat(ui): AI-Enhanced Dialogue toggle + hardware detection (#646, D-138)

Implements the full AI-Enhanced Dialogue feature for Sprint 26:

- HardwareDetector autoload (extends Node): three-layer detection —
  Layer 1 RAM classification (pass/marginal/fail, thresholds 2GB/1.6GB),
  Layer 2 TPT benchmark cache (green/yellow/red, thresholds 6/3 t/s),
  Layer 3 degradation monitoring (>40% drop → yellow). load_ai_pref()
  restores toggle state from user://settings.cfg on startup.

- Settings dialog AI section: toggle, colored status dot, status message
  label, testable API (get_ai_dialogue_label_text, set_ai_dialogue_
  hardware_status, is_ai_dialogue_toggle_enabled). Only RAM "fail" greys
  out toggle — player always overrides yellow/red recommendations (D-138).

- GameState.ai_enhanced_dialogue_enabled (default true, opt-out model).
  GameState.settings_response (v20 one-shot settings dump from server).
  apply_snapshot() hydrates ai_enhanced_dialogue_enabled from full dump.

- Protocol v19→v20, settings_response decoding in decode_snapshot().
  Protocol converted to extends Node autoload (enables test has_method).
  encode_change_settings() helper for test inspection.

- InputMapper: CHANGE_SETTINGS, REQUEST_ALL_SETTINGS, DELETE_SETTING.
  SimBridge: wire mappings for all three. RequestAllSettings queued after
  handshake to hydrate client state from server SQLite on connect.
  settings_response carry-forward in receive_bytes().

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

client/project.godot

@@ -17,6 +17,7 @@ config/icon="res://icon.svg"
 
 [autoload]
 
+Protocol="*res://scripts/protocol/protocol.gd"
 SimBridge="*res://scripts/autoloads/sim_bridge.gd"
 GameState="*res://scripts/autoloads/game_state.gd"
 InputMapper="*res://scripts/autoloads/input_mapper.gd"
@@ -24,6 +25,7 @@ UIStrings="*res://scripts/autoloads/ui_strings.gd"
 FogState="*res://scripts/autoloads/fog_state.gd"
 AudioManager="*res://scripts/autoloads/audio_manager.gd"
 SessionManager="*res://scripts/autoloads/session_manager.gd"
+HardwareDetector="*res://ui/hardware_detector.gd"
 
 [audio]