I-4: distinguish a mirror that never ran from one that is behind

Gitea reports the epoch for 'not yet synced', which arithmetic turns into a
56-year lag and a confident 'degraded'. Collapsing those two states is how a
backup that was never made gets read as a backup that is merely stale — which
is the more dangerous direction, because 'behind' sounds survivable.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

api/app/routes/repos.py

@@ -514,6 +514,7 @@ async def mirror_status(
         "healthy": "A second copy of this project is up to date.",
         "degraded": "The second copy is behind. Your work here is safe.",
         "absent": "There is no second copy of this project yet.",
+        "pending": "The second copy is set up and hasn't run yet.",
         "unconfigured": "Off-site copies aren't switched on yet.",
         "unknown": "We can't tell how the second copy is doing right now.",
     }[status["state"]]