Keep single-device circuit names equal to their device row

A circuit with exactly one device row and no fed distribution board is
shown as that row, so its own name was hidden and could drift (e.g.
"Neuer Stromkreis" in the print view). Commands that create or leave
such a circuit, rename its row or unlink its downstream board now set
the circuit name to the row name and store the change as optional
circuitDisplayNames, so Undo restores an overwritten free name exactly.
Migration 0016 aligns existing data.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/db/migrations/meta/_journal.json

@@ -113,6 +113,13 @@
       "when": 1790773066696,
       "tag": "0015_wide_night_thrasher",
       "breakpoints": true
+    },
+    {
+      "idx": 16,
+      "version": "6",
+      "when": 1793277078601,
+      "tag": "0016_single_device_circuit_names",
+      "breakpoints": true
     }
   ]
 }