Compressing shows no progress

[sarensw]

Compressing gives no progress feedback. Drop a 2.6 GB folder on the Quick Compress
window or the start page's compress area and nothing happens on screen until the
archive appears — the UI stays responsive, but there is no bar, no byte count, and
no signal that it finished.

Extraction already has all of this: ExtractionProgressCenter drives a window that
auto-shows on an active job, shows a bar, a speed graph and an ETA, auto-closes when
done, and stays open on failure. Compression should reuse it.

Why this is mostly plumbing

ExtractionJob is a byte-transfer model, not an extraction-specific one —
archiveName, destination, itemCount, totalBytes, completedBytes,
state {running, done, failed, cancelled}, speed samples, ETA.

The data already lines up. The center takes:

reportEngineProgress(_ id: UUID, completed: Int64, total: Int64)

and ArchiveState.save() already receives exactly that from 7-Zip, then discards it:

let onWriteProgress: @Sendable (UInt64, UInt64) -> Bool = { completed, total in
    let pct = Int((completed * 100) / total)   // bytes thrown away here

The progress view needs no wording changes either: its only localized string is
"\(formatDuration(remaining)) left". Everything else is names, sizes and speeds.

Scope

• ArchiveState.save() reports bytes, not just a percentage
• DropCompressor calls begin() / finish() on the center
• Compute totalBytes from the dropped files, or pass nil and let
  engineTotalBytes supersede it once the engine reports (the model already
  handles both)
• Restore the running row in the drop window — the filter that hides finished
  successes also hides .running, so the ProgressView in DropJobRow can
  never appear

Both surfaces are affected: the Quick Compress window and the start page's compress
area.

Deliberately out of scope

Each of these spills past the plumbing and is worth its own decision:

1. Naming. Everything is Extraction*, including ExtractionProgressCenter.shared.
   Compression joining it either lives with the name or forces a rename across every
   extraction call site.
2. Quit guard. applicationShouldTerminate refuses on hasActiveJobs with
   "An extraction is still in progress". Compress jobs would inherit that wording —
   right behaviour, wrong sentence.
3. Cancellation. Wireable: save()'s progress callback returns Bool, and false
   aborts the write. But that leaves a partial archive on disk to clean up, which is
   new behaviour rather than reuse.
4. DropJob becomes redundant once the center tracks compress jobs — the drop
   window's own row model duplicates it.