v0.7.4 — desktop bulk copy, bulk-transfer preview, and hardware-caught fixes

v0.7.4 — desktop bulk copy, bulk-transfer preview, and two real bugs a hardware run caught

Desktop reaches CLI parity for bulk driver export. This PC → Copy all
printers... exports every supported queue on the machine to its own .ssb
file, sharing the exact bundle.CreateAll batch implementation copy --all
already used on the CLI rather than a second one: a destination folder, an
include-driver choice, live progress, a Stop copying control that keeps
whatever already finished, and Copy results / JSON for pasting the outcome
into a ticket. Existing files are never replaced, and a filename collision is
reported before the affected printer is probed or its driver exported.

Bulk saved-setup transfer gets a real preview. profile export-all /
profile import-all take a new --dry-run on the CLI; the desktop's Saved
setups → Export/Import all JSON gained the same review step. Both list every
filename, printer setting and destination conflict before anything is
written, and closing that review dialog no longer blocks indefinitely if a
destination check or save is slow — a stalled network path used to trap the
operator with no way out short of killing the app.

A quality pass over the diff, then a hardware run on real Windows, found and
fixed:

• spoolsmith copy --all could silently swap its documented JSON result shape
  for a generic error object when the output folder couldn't be created or
  read, discarding the per-queue outcomes it had already built.
• A single copy's destination-filename collision was only caught after
  probing the printer and, with --include-driver, exporting the driver —
  copy --all already checked first; copy now does too.
• Two GUI buttons had silently regressed to "Export/Import setup JSON..."
  — misleading, since they act on every saved profile in the folder, not the
  one selected above them — caught only because this release's full 31-test
  FlaUI suite was actually run against real Windows before shipping, not just
  reviewed as a diff.

Full account, including what a static review can't catch and what only
running the app on real hardware does, in
docs/dev-process.md.
Verified: gofmt/go build/go vet/go test clean on Linux and
cross-compiled for Windows; all 31 SpoolSmithGui.Tests FlaUI tests passing
against the real rendered GUI on the kubert Windows 11 box.