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/note-input.tsx

@@ -434,6 +434,38 @@ export function NoteInput({
     e.target.value = ''
   }
 
+  const uploadImageFile = async (file: File) => {
+    const formData = new FormData()
+    formData.append('file', file)
+    const response = await fetch('/api/upload', { method: 'POST', body: formData })
+    if (!response.ok) throw new Error('Upload failed')
+    const data = await response.json()
+    return data.url
+  }
+
+  // Paste handler: upload clipboard images
+  useEffect(() => {
+    const handlePaste = async (e: ClipboardEvent) => {
+      const items = e.clipboardData?.items
+      if (!items) return
+      for (const item of Array.from(items)) {
+        if (item.type.startsWith('image/')) {
+          e.preventDefault()
+          const file = item.getAsFile()
+          if (!file) continue
+          try {
+            const url = await uploadImageFile(file)
+            setImages(prev => [...prev, url])
+          } catch {
+            toast.error(t('notes.uploadFailed', { filename: 'pasted image' }))
+          }
+        }
+      }
+    }
+    document.addEventListener('paste', handlePaste)
+    return () => document.removeEventListener('paste', handlePaste)
+  }, [t])
+
   const handleAddLink = async () => {
     if (!linkUrl) return
 
@@ -927,6 +959,7 @@ export function NoteInput({
           onClose={() => setAiOpen(false)}
           noteTitle={title}
           noteContent={content}
+          noteImages={images}
           onApplyToNote={(newContent) => setContent(newContent)}
           lastActionApplied={false}
           notebooks={notebooks.map(nb => ({ id: nb.id, name: nb.name }))}