Fix: comprehensive bug review — restore refactor regressions & fix critical/major/minor bugs

Critical:
- responseExtractor.js: fix import depth (7x ../ -> 6x) that broke the module
  graph for encounters, separate/external generation, and auto-avatars
- settingsListeners.js: restore ~25 undefined functions, ~40 lost event
  bindings, and the entire 'Initialize UI state' block dropped by the c14c141
  refactor; add initializeSettingsUIState()
- Restore all External API mode handlers (base-url, api-key, model,
  max-tokens, temperature, key-visibility, test-connection) + value init
- validator.js: convert CJS->ESM (crashed under type:module), fix
  glob.sync->globSync (v13 API), fix '!key in obj' precedence bugs

Major:
- sillytavern.js: add missing updateMessageBlock import
- infoBox.js: add missing saveSettings import
- userStats.js: fix double-escaped quantity regex

Minor:
- config.js: settingsVersion 6->7, restore showLockIcons, fix apiKey comment
- events.js: off() tracking + unregister/re-register on disable/enable
- escapeHtml: escape quotes (XSS) in all 3 copies
- template.html: data-prompt dialogue-coloring -> dialogueColoring
- trackerEditor.js: stale externalApiOnly -> sendAllEnabledOnRefresh
- suppression.js: fix '[object Object]' on empty instruct value
- persistence.js: await migrateToV3JSON (loadSettings now async)
- weatherEffects.js: JSON.parse -> repairJSON
- mobile.js: fix corrupted comment line
- Add missing debugMode setting; settings.html v3.7.2 -> v3.7.4

Dead code removed:
- Unused imports/vars (promptBuilder, jsonPromptHelpers, encounterPrompts,
  injector), withChangeDetection, trackJQueryHandler/cleanupJQueryEvents,
  renderThoughtsSidebarOnly, updateCheckpointButtonInMenu, addDiceQuickReply,
  setupRefreshButtonDrag/setupDebugButtonDrag (~430 lines)

Verified: 78/78 tests pass, style.css in sync, validator runs clean.

src/systems/ui/checkpointUI.js

@@ -339,31 +339,4 @@ function processExpandedButton(messageBlock) {
 }
 
 
-/**
- * Update the checkpoint button in an existing menu
- * @param {HTMLElement} menu - The extraMesButtons or mes_buttons container
- * @param {number} messageId - The message index
- */
-function updateCheckpointButtonInMenu(menu, messageId) {
-    if (!menu) return;
 
-    // Find the checkpoint button (either dropdown or expanded)
-    const existingButton = menu.querySelector('.rpg-checkpoint-button, .rpg-checkpoint-button-expanded');
-    if (!existingButton) return;
-
-    const isCheckpoint = isCheckpointMessage(messageId);
-
-    // Update icon
-    const icon = existingButton.querySelector('i');
-    if (icon) {
-        icon.className = isCheckpoint ? 'fa-solid fa-bookmark' : 'fa-regular fa-bookmark';
-        icon.style.color = isCheckpoint ? '#4a9eff' : '';
-    }
-
-    // Update tooltip
-    existingButton.title = isCheckpoint
-        ? 'Clear Chapter Start'
-        : 'Set Chapter Start — When bookmarked, this message will count as the first message in the chat history, skipping earlier ones.';
-    const translationKey = isCheckpoint ? 'checkpoint.clearChapterStart' : 'checkpoint.setChapterStart';
-    existingButton.setAttribute('data-i18n', translationKey);
-}