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/scripts/autoloads/input_mapper.gd

@@ -25,6 +25,9 @@ enum Action {
 	SAVE_GAME,  # #554: F5 quicksave — sends SaveGame to server with save path
 	LOAD_GAME,  # #554: F6 quickload — sends LoadGame to server with save path
 	DEBUG_COMMAND,  # #581: debug console command dispatch — sends DebugCommandKind to server
+	CHANGE_SETTINGS,      # #646: persist a setting to server SQLite — sends {key, value} to server
+	REQUEST_ALL_SETTINGS, # #646: request full settings dump from server after handshake (unit variant)
+	DELETE_SETTING,       # #646: delete a setting by key from server SQLite (struct variant)
 }
 
 var input_queue: Array[Dictionary] = []