Reformat progress lines and prune output

Progress lines now use the form:
  ..., <subject> elapsed: <dur>, <subject> ETA: <time> (est remain <dur>).

ui.Time formats same-day times as HH:MM:SS and other-day times as
YYYY-MM-DD HH:MM:SS, with no timezone suffix (local time is implied).

The local-index-database prune complete line now shows remaining
counts for each category:
  ... 1 incomplete snapshots removed (3 remain), 3783 orphaned files
  removed (42 remain), ...

internal/ui/ui.go

@@ -188,9 +188,17 @@ func (w *Writer) Duration(d time.Duration) string {
 	return w.paint(ansiYellow, d.Round(time.Second).String())
 }
 
-// Time colorizes an absolute time (RFC3339, second precision).
+// Time colorizes an absolute clock time. If t falls on today's local
+// calendar date the output is "HH:MM:SS"; otherwise it is
+// "YYYY-MM-DD HH:MM:SS". No timezone is included — values are
+// displayed in the process's local zone.
 func (w *Writer) Time(t time.Time) string {
-	return w.paint(ansiYellow, t.Format(time.RFC3339))
+	t = t.Local()
+	now := time.Now()
+	if t.Year() == now.Year() && t.YearDay() == now.YearDay() {
+		return w.paint(ansiYellow, t.Format("15:04:05"))
+	}
+	return w.paint(ansiYellow, t.Format("2006-01-02 15:04:05"))
 }
 
 // Count colorizes an integer count with thousands separators.