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), ...

README.md

@@ -421,12 +421,13 @@ Conventions:
   "Uploaded" for Complete. Never write the words "begin" or "complete"
   in the body — the marker color already conveys that.
 * All elapsed and remaining-time fields are explicitly scoped to their
-  subject: write "blob upload elapsed 30s, blob upload estimated remaining
-  time (14s), finish at 2026-06-17T03:15:00Z", never just "elapsed 30s,
-  ETA 14s".
+  subject: write "blob upload elapsed: 30s, blob upload ETA: 03:15:00
+  (est remain 14s)", never just "elapsed 30s, ETA 14s".
 * "ETA" means an absolute clock time (when the operation will finish),
   not a remaining-duration. Use `ui.Time()` for the former and
   `ui.Duration()` for the latter, and label both.
+* `ui.Time` formats same-day times as `HH:MM:SS` and other-day times as
+  `YYYY-MM-DD HH:MM:SS`. No timezone — local time is implied.
 
 Value colorizers in `internal/ui` colorize specific value types
 consistently. Compose messages from these helpers rather than embedding