KI-AGENT: Ergänze fehlende Profil-Verfügbarkeitsmigration

backend/db/migrations/0042_profile_availability_note.sql

@@ -0,0 +1,2 @@
+ALTER TABLE "auth_profiles"
+ADD COLUMN IF NOT EXISTS "availability_note" text;

backend/db/migrations/meta/_journal.json

@@ -295,6 +295,13 @@
       "when": 1780149600000,
       "tag": "0041_profile_calendar_subscription",
       "breakpoints": true
+    },
+    {
+      "idx": 42,
+      "version": "7",
+      "when": 1780153200000,
+      "tag": "0042_profile_availability_note",
+      "breakpoints": true
     }
   ]
 }