feat: chat stop button, image paste, vision AI, search fixes

- Add stop button to all chat interfaces (floating, contextual, full-page)
- Add conversation sliding window (50 messages) to prevent context overflow
- Add chat timeout warning (30s toast)
- Force response language in chat system prompt (mandatory per-locale)
- Add image paste from clipboard in all note editors (card, list, input)
- Fix upload API to infer extension from MIME type for clipboard images
- Add image description support in note AI chat (base64 vision)
- Fix search regex crash on special characters (escape user input)
- Fix search case-insensitivity on PostgreSQL (mode: 'insensitive')
- Add try/catch around semantic search in chat route (prevent blocking)
- Add new chat button to floating AI assistant
- Fix empty thinking bubbles for reasoning models (filter non-text parts)
- Remove duplicate AI assistant toggle from note editor header
- Improve link metadata scraping (timeout, content-type check, relative URLs)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/components/contextual-ai-chat.tsx

@@ -7,7 +7,7 @@ import type { UIMessage } from 'ai'
 import { cn } from '@/lib/utils'
 import { Button } from '@/components/ui/button'
 import {
-  X, Bot, Sparkles, Send, Loader2,
+  X, Bot, Sparkles, Send, Loader2, Square,
   Briefcase, Palette, GraduationCap, Coffee,
   Lightbulb, Minimize2, AlignLeft, Wand2,
   Globe, BookOpen, FileText, RotateCcw, Check,
@@ -70,6 +70,7 @@ interface ContextualAIChatProps {
   onClose: () => void
   noteTitle?: string
   noteContent?: string
+  noteImages?: string[]
   /** Called when an action result should be injected into the note */
   onApplyToNote?: (newContent: string) => void
   /** Called when the user wants to undo the last injected action */
@@ -88,6 +89,7 @@ export function ContextualAIChat({
   onClose,
   noteTitle,
   noteContent,
+  noteImages,
   onApplyToNote,
   onUndoLastAction,
   lastActionApplied = false,
@@ -115,7 +117,12 @@ export function ContextualAIChat({
   const buildChatBody = () => {
     const body: Record<string, any> = { language, webSearch }
     if (chatScope === 'note') {
-      body.noteContext = { title: noteTitle || '', content: noteContent || '', tone: selectedTone }
+      body.noteContext = {
+        title: noteTitle || '',
+        content: noteContent || '',
+        tone: selectedTone,
+        images: noteImages || [],
+      }
     } else if (chatScope !== 'all') {
       // scope is a notebook ID
       body.notebookId = chatScope
@@ -123,7 +130,7 @@ export function ContextualAIChat({
     return body
   }
 
-  const { messages, sendMessage, status } = useChat({ transport })
+  const { messages, sendMessage, status, stop } = useChat({ transport })
 
   const isLoading = status === 'submitted' || status === 'streaming'
 
@@ -273,6 +280,8 @@ export function ContextualAIChat({
 
             {messages.map((msg: UIMessage) => {
               const content = getMessageContent(msg)
+              // Skip empty assistant messages (thinking/reasoning phase)
+              if (msg.role === 'assistant' && !content) return null
               return (
                 <div key={msg.id} className={cn('flex gap-2', msg.role === 'user' && 'flex-row-reverse')}>
                   <div className={cn(
@@ -414,14 +423,24 @@ export function ContextualAIChat({
                     </button>
                   )}
                 </div>
-                <Button
-                  size="icon"
-                  className="h-7 w-7 rounded-lg bg-primary text-primary-foreground shadow-sm disabled:opacity-50"
-                  onClick={handleSend}
-                  disabled={isLoading || !input.trim()}
-                >
-                  {isLoading ? <Loader2 className="h-3.5 w-3.5 animate-spin" /> : <Send className="h-3.5 w-3.5 ml-0.5" />}
-                </Button>
+                {isLoading ? (
+                  <Button
+                    size="icon"
+                    className="h-7 w-7 rounded-lg bg-red-500 text-white shadow-sm hover:bg-red-600"
+                    onClick={() => stop()}
+                  >
+                    <Square className="h-3.5 w-3.5" />
+                  </Button>
+                ) : (
+                  <Button
+                    size="icon"
+                    className="h-7 w-7 rounded-lg bg-primary text-primary-foreground shadow-sm disabled:opacity-50"
+                    onClick={handleSend}
+                    disabled={!input.trim()}
+                  >
+                    <Send className="h-3.5 w-3.5 ml-0.5" />
+                  </Button>
+                )}
               </div>
             </div>
             <p className="text-[9px] text-muted-foreground/40 text-center mt-1">{t('ai.newLineHint')}</p>