T4.2: Extract jobs_view.go (list + details + toolbar)

Move the jobs list, details panel, folder filter, toolbar buttons, and
all related helpers out of mainwindow.go into the new jobs_view.go.
newMainView now calls newJobsView(w, svc) which returns a panel and a
refresh closure; the subscriber and history wiring remain in mainwindow.go.

showJobDialog lives in jobs_view.go as a temporary home until T4.3
extracts it to job_dialog.go.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/REFACTORING.md

@@ -269,7 +269,7 @@ Track progress here. Mark tasks complete as they land and pass review.
 
 ### Phase 4 — Carve up the GUI
 - [x] T4.1 — Rename `gui` → `ui`; split app.go into run.go + mainwindow.go _(required Fyne v2.5.3→v2.6.3 upgrade for `fyne.Do`)_
-- [ ] T4.2 — Extract `jobs_view.go`
+- [x] T4.2 — Extract `jobs_view.go`
 - [ ] T4.3 — Extract `job_dialog.go`
 - [ ] T4.4 — Extract `history_view.go`
 - [ ] T4.5 — Extract `settings_view.go`