fix(butler): wire verification gaps — pain storage init, cold start, UI mode switches

- Call init_pain_storage() in Tauri .setup() so pain persistence activates on boot
- Integrate useColdStart hook into FirstConversationPrompt for auto-greeting
- Add UI mode toggle section to Settings/General (already had imports)
- Add "简洁" mode switch-back button to TopBar in professional layout
- Update SemanticSkillRouter @reserved annotation to reflect active status

desktop/src/components/FirstConversationPrompt.tsx

@@ -7,6 +7,7 @@
  * - Horizontal quick-action chips (colored pills)
  * - Clean, minimal aesthetic
  */
+import { useEffect } from 'react';
 import { motion } from 'framer-motion';
 import {
   Sparkles,
@@ -21,6 +22,7 @@ import {
   generateWelcomeMessage,
   getScenarioById,
 } from '../lib/personality-presets';
+import { useColdStart } from '../lib/use-cold-start';
 import type { Clone } from '../store/agentStore';
 import { useChatStore } from '../store/chatStore';
 import { useClassroomStore } from '../store/classroomStore';
@@ -56,6 +58,16 @@ export function FirstConversationPrompt({
   onSelectSuggestion,
 }: FirstConversationPromptProps) {
   const chatMode = useChatStore((s) => s.chatMode);
+  const { isColdStart, phase, greetingSent, markGreetingSent, getGreetingMessage } = useColdStart();
+
+  // Cold start: auto-trigger greeting for first-time users
+  useEffect(() => {
+    if (isColdStart && phase === 'idle' && !greetingSent) {
+      const greeting = getGreetingMessage(clone.nickname || clone.name, clone.emoji);
+      onSelectSuggestion?.(greeting);
+      markGreetingSent();
+    }
+  }, [isColdStart, phase, greetingSent, clone.nickname, clone.name, clone.emoji, onSelectSuggestion, markGreetingSent, getGreetingMessage]);
 
   const modeGreeting: Record<string, string> = {
     flash: '快速回答，即时响应',