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/data/ui-strings.yaml

@@ -194,6 +194,11 @@ settings:
   text_speed: "Text Speed"
   fullscreen: "Fullscreen"
   language: "Language"
+  # #646: AI-Enhanced Dialogue toggle (D-138)
+  ai_section_header: "AI DIALOGUE"
+  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."
 
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 # CHARACTER SELECTION (if applicable in v0.1)