Franklin Agent 3.25.1 — fix image paste on Linux terminals

3.25.0 only probed the system clipboard for an image when the bracketed-paste
buffer arrived empty. That holds for macOS Terminal/iTerm2 but breaks on
several Linux terminals (reported on Kali): they send a filename, a file://
URI, or a raw image header alongside the paste, so the non-empty buffer made the
gate skip the probe and the image was silently dropped.

• The clipboard is now always probed on paste-end, regardless of buffer
  contents. If an image is found it wins and the bracketed-paste stub is
  dropped; otherwise the existing text-paste path (collapse-to-block or inline)
  runs unchanged. Verified in a Lima Ubuntu VM with a real PNG on the X11
  clipboard — all buffer shapes (empty / filename / URI / header) now attach the
  image. (#77)