fix(v2): preserve replay attachments in fallback prompt translation

Map non-text prompt parts (images/files) into v2 prompt files entries in
the client shim so the foreground-fallback replay no longer silently
drops attachment content; parts without a derivable uri are logged and
skipped. Also correct the pinned-version examples (2.0.3 -> 2.2.17) in
README and the v2 compatibility doc.