feat(react-ui/chat): paste images from clipboard into chat input (#10428)

The chat input only accepted attachments via the file picker, so users
who copied an image from a webpage or a screen region had to first save
it to a file before attaching it (#10361).

Add an onPaste handler on the input textarea that pulls image items out
of the clipboard and routes them through the same staging path as the
file picker. The per-file processing in handleFileChange is extracted
into a shared processFiles helper so both entry points stay in sync.
Clipboard images, which arrive unnamed or as a generic "image.png", are
given unique typed names so multiple pastes don't collide, and the
default paste is suppressed only when an image is actually attached so
normal text paste is unaffected.

Closes #10361

Signed-off-by: Anai-Guo <antai12232931@outlook.com>

Author: Anai-Guo

core/http/react-ui/src/pages/Chat.jsx

@@ -742,6 +742,27 @@ export default function Chat() {
     e.target.value = ''
   }, [])
 
+  const handlePaste = useCallback(async (e) => {
+    const items = e.clipboardData?.items
+    if (!items) return
+    const images = Array.from(items)
+      .filter(item => item.kind === 'file' && item.type.startsWith('image/'))
+      .map(item => item.getAsFile())
+      .filter(Boolean)
+    if (images.length === 0) return
+    // A pasted image attaches as a file rather than inserting into the text.
+    e.preventDefault()
+    // Clipboard images arrive unnamed or as a generic "image.png"; give each
+    // a unique, typed name so multiple pastes don't collide.
+    const newFiles = await Promise.all(images.map(async (file, i) => {
+      const name = (file.name && file.name !== 'image.png')
+        ? file.name
+        : `pasted-image-${i + 1}.${(file.type.split('/')[1] || 'png').replace('+xml', '')}`
+      return { name, type: file.type, base64: await fileToBase64(file) }
+    }))
+    setFiles(prev => [...prev, ...newFiles])
+  }, [])
+
   const handleSend = useCallback(async () => {
     const msg = input.trim()
     if (!msg && files.length === 0) return
@@ -1391,6 +1412,7 @@ export default function Chat() {
               value={input}
               onChange={(e) => setInput(e.target.value)}
               onKeyDown={handleKeyDown}
+              onPaste={handlePaste}
               placeholder={t('input.placeholder')}
               rows={1}
               disabled={isStreaming}