feat(core,fuse,cli): reuse cached content and take several sources in moves

- A mirror download first copies the file out of the content cache when the
  same revision is cached whole or block by block, so moving a file out of an
  on-demand folder into a mirror costs no traffic for what was already read.
- `pdfs move a b c DEST` moves every source, reports each failure and exits
  non-zero if any failed.
- Mirror-to-mirror moves rename with RENAME_NOREPLACE, so a name that
  appeared at the destination after the check is never overwritten.
- The local copy a move out of a mirror drops is checked again just before
  it is deleted; anything written into it meanwhile keeps the copy and is
  uploaded as new by the next pass.

docs/CHANGELOG.md

@@ -20,6 +20,10 @@ scratch (user data in `staging/` and `recovery/` is never touched by this).
   level. A move is refused, with the reason, when the source still has changes that are not on
   Proton Drive, when the two locations are on different volumes, or when a synced folder stays
   busy with a sync pass.
+- **`pdfs move` takes several sources.** `pdfs move a b c DEST` moves all three and
+  reports each one that could not move.
+- **Moving into a mirrored folder reuses cached content.** A file already cached by
+  an online-only folder is copied into place instead of downloaded again.
 
 ## [2.6.2] — 2026-09-28