fix(admin): drop sidebar reference from welcome subtitle

The admin overview welcome copy read "Pick a section from the
sidebar to manage HealthLog." but the mobile admin shell uses a
horizontal pill strip, not a sidebar — so the instruction was
literally wrong on the screen size where it mattered most. Drop
the surface reference and let the copy work on every layout.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

messages/de.json

@@ -1810,7 +1810,7 @@
     },
     "overview": {
       "welcomeTitle": "Willkommen, {name}",
-      "welcomeSubtitle": "Du bist als Administrator angemeldet. Wähle einen Bereich in der Seitenleiste, um HealthLog zu verwalten.",
+      "welcomeSubtitle": "Du bist als Administrator angemeldet. Wähle einen Bereich, um HealthLog zu verwalten.",
       "snapshotTitle": "System-Snapshot",
       "snapshotVersion": "Version",
       "snapshotDatabase": "Datenbank",

messages/en.json

@@ -1810,7 +1810,7 @@
     },
     "overview": {
       "welcomeTitle": "Welcome, {name}",
-      "welcomeSubtitle": "You are signed in as administrator. Pick a section from the sidebar to manage HealthLog.",
+      "welcomeSubtitle": "You are signed in as administrator. Pick a section to manage HealthLog.",
       "snapshotTitle": "System snapshot",
       "snapshotVersion": "Version",
       "snapshotDatabase": "Database",