Say why Transit and Bike Share rows are empty outside coverage

Over a city with no feed or system (London, Tokyo) both rows read
"ON · — · never", the same as a feed that never answered. Transit already
computed a coverage note but put it only in `coverage`, which the row does
not show; Bike Share reported nothing at all.

Both layers now report a `zoom-in` guidance status with a `statusMessage`:
"Fly below 3,000 km to a covered region" / "No feed here yet · N regions
available" for Transit, and "Fly below 48 km to a covered city" / "No bike
share here yet · N systems available" for Bike Share. A loading or failed
Bike Share city keeps its own text. Leaving coverage clears the layer's
last-update time, so the row no longer dates data it no longer draws.

The coverage-note translations move from the voice card into
`translateStatusMessage` (ui/statusText.js), which the Layers row and the
voice card now share.

src/i18n/locales/de.json

@@ -2662,6 +2662,11 @@
     "one": "Hier noch kein Feed · {n} Region verfügbar",
     "other": "Hier noch kein Feed · {n} Regionen verfügbar"
   },
+  "Fly below {km} km to a covered city": "Unter {km} km Höhe zu einer abgedeckten Stadt fliegen",
+  "No bike share here yet · {n} systems available": {
+    "one": "Hier noch kein Bikesharing · {n} System verfügbar",
+    "other": "Hier noch kein Bikesharing · {n} Systeme verfügbar"
+  },
   "degraded": "eingeschränkt",
   "stale": "veraltet",
   "partial": "teilweise",