mirror: true overall progress via --check-first + visible scan phase

With SFTP remotes rclone lists the tree while transferring, so the
`Transferred:` total grows during the run: the first ticks showed a
single file's percentage (e.g. 2.9 MiB / 8.6 MiB, 35%) which then
collapsed to 0% once the real 113 GiB total appeared. That is what
looked like "progress per album".

- pass --check-first: rclone finishes the remote listing before any
  transfer starts, so the byte total is final and the gauge is a true
  overall percentage for the whole mirror
- while scanning, no bytes move yet, so the panel now shows
  `Scanning remote · 11,810 items listed` and `0 B / 113 GiB to transfer`
  (parsed from rclone's `Checks: … Listed N`) instead of a bogus 0% bar
- once transfers start the display switches back to percentage +
  bytes + current file

Verified against the real storagebox remote (capped with
RCLONE_MAX_TRANSFER): scan ticks show listed counts climbing to 11,810
with the pending total, then transfers show `9.984 MiB / 113.477 GiB`
with the final denominator and no per-file percentage jumps.

Bump to 0.3.2.

Cargo.lock

@@ -253,7 +253,7 @@ dependencies = [
 
 [[package]]
 name = "dap-tui"
-version = "0.3.1"
+version = "0.3.2"
 dependencies = [
  "anyhow",
  "chrono",