paste: when the clipboard carries files, never let the HTML/URL fragment into the composer (#132)

Verified headless that pasting an image copied from a web page (bitmap +
text/html <img src alt> + text/plain URL) already produced only the upload
card and an empty composer; make that explicit with a preventDefault so a
future editor change can't regress it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/hooks/useFilePasteHandler.ts

@@ -5,7 +5,14 @@ export const useFilePasteHandler = (onPaste: (file: File[]) => void): ClipboardE
   useCallback(
     (evt) => {
       const files = getDataTransferFiles(evt.clipboardData);
-      if (files) onPaste(files);
+      if (files) {
+        // [Gitea #132] An image copied from a web page arrives with a
+        // text/html `<img src=… alt=…>` fragment and a text/plain URL beside
+        // the bitmap. Only the file is wanted — stop the editor's own
+        // HTML/text insertion so nothing else lands in the composer.
+        evt.preventDefault();
+        onPaste(files);
+      }
     },
     [onPaste],
   );