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/chat/chat-container.tsx

@@ -40,6 +40,7 @@ export function ChatContainer({ initialConversations, notebooks, webSearchAvaila
     sendMessage,
     status,
     setMessages,
+    stop,
   } = useChat({
     transport,
     onError: (error) => {
@@ -49,6 +50,15 @@ export function ChatContainer({ initialConversations, notebooks, webSearchAvaila
 
   const isLoading = status === 'submitted' || status === 'streaming'
 
+  // Timeout warning: show toast if response takes > 30s
+  useEffect(() => {
+    if (!isLoading) return
+    const timer = setTimeout(() => {
+      toast.warning(t('chat.timeoutWarning') || 'Response is taking longer than expected...')
+    }, 30000)
+    return () => clearTimeout(timer)
+  }, [isLoading, t])
+
   // Sync historyMessages after each completed streaming response
   // so the display doesn't revert to stale history
   useEffect(() => {
@@ -190,6 +200,7 @@ export function ChatContainer({ initialConversations, notebooks, webSearchAvaila
             <ChatInput
               onSend={handleSendMessage}
               isLoading={isLoading}
+              onStop={stop}
               notebooks={notebooks}
               currentNotebookId={selectedNotebook || null}
               webSearchEnabled={webSearchEnabled}

memento-note/components/chat/chat-input.tsx

@@ -1,7 +1,7 @@
 'use client'
 
 import { useState, useRef, useEffect } from 'react'
-import { Send, BookOpen, X, Globe } from 'lucide-react'
+import { Send, BookOpen, X, Globe, Square } from 'lucide-react'
 import { getNotebookIcon } from '@/lib/notebook-icon'
 import { Button } from '@/components/ui/button'
 import { Textarea } from '@/components/ui/textarea'
@@ -19,6 +19,7 @@ import { useLanguage } from '@/lib/i18n'
 interface ChatInputProps {
   onSend: (message: string, notebookId?: string) => void
   isLoading?: boolean
+  onStop?: () => void
   notebooks: any[]
   currentNotebookId?: string | null
   webSearchEnabled?: boolean
@@ -26,7 +27,7 @@ interface ChatInputProps {
   webSearchAvailable?: boolean
 }
 
-export function ChatInput({ onSend, isLoading, notebooks, currentNotebookId, webSearchEnabled, onToggleWebSearch, webSearchAvailable }: ChatInputProps) {
+export function ChatInput({ onSend, isLoading, onStop, notebooks, currentNotebookId, webSearchEnabled, onToggleWebSearch, webSearchAvailable }: ChatInputProps) {
   const { t } = useLanguage()
   const [input, setInput] = useState('')
   const [selectedNotebook, setSelectedNotebook] = useState<string | undefined>(currentNotebookId || undefined)
@@ -123,18 +124,28 @@ export function ChatInput({ onSend, isLoading, notebooks, currentNotebookId, web
             )}
           </div>
 
-          {/* Send Button */}
-          <Button 
-            disabled={!input.trim() || isLoading}
-            onClick={handleSend}
-            size="icon"
-            className={cn(
-              "rounded-full h-8 w-8 transition-all duration-200",
-              input.trim() ? "bg-primary text-primary-foreground shadow-sm hover:scale-105" : "bg-slate-200 dark:bg-slate-700 text-slate-400 dark:text-slate-500"
-            )}
-          >
-            <Send className="h-4 w-4 ml-0.5" />
-          </Button>
+          {/* Send / Stop Button */}
+          {isLoading && onStop ? (
+            <Button
+              onClick={onStop}
+              size="icon"
+              className="rounded-full h-8 w-8 bg-red-500 text-white shadow-sm hover:bg-red-600 transition-all duration-200"
+            >
+              <Square className="h-3.5 w-3.5" />
+            </Button>
+          ) : (
+            <Button
+              disabled={!input.trim() || isLoading}
+              onClick={handleSend}
+              size="icon"
+              className={cn(
+                "rounded-full h-8 w-8 transition-all duration-200",
+                input.trim() ? "bg-primary text-primary-foreground shadow-sm hover:scale-105" : "bg-slate-200 dark:bg-slate-700 text-slate-400 dark:text-slate-500"
+              )}
+            >
+              <Send className="h-4 w-4 ml-0.5" />
+            </Button>
+          )}
         </div>
       </div>