fix(fires): reject rolled-over acquisition dates and document UTC times

changelog.d/1395-fires-tool-acquired-time.md

@@ -1,4 +1,6 @@
 - Report a fire detection's acquisition time as a UTC timestamp in
   `get_active_fires`. The tool joined FIRMS's unpadded date and time, so a
   00:45 UTC detection read "2026-01-01 45"; it now reads
-  `2026-01-01T00:45:00.000Z` (Rudy Celekli, @rudycelekli, #1395).
+  `2026-01-01T00:45:00.000Z`. Missing or invalid dates and times remain
+  unknown rather than rolling into another calendar day
+  (Rudy Celekli, @rudycelekli, #1395).