fix(presence): missing imports in 3 endpoints

Same pattern as touchLastSeen: getLastSeenBatch, setPresenceVisible,
getFollowingIds wurden im db/profile.ts implementiert aber nicht in den
Endpoints importiert. Alle 3 warfen 500 ReferenceError → grüner Dot
zeigte sich nie + Toggle silently failed.

Nitro's auto-import covered nur defineEventHandler/getQuery etc., NICHT
unsere eigenen db-layer helper.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/server/api/me/following.get.ts

@@ -11,6 +11,7 @@
  *   { userIds: string[] }
  */
 import { requireUser } from "../../utils/auth";
+import { getFollowingIds } from "../../db/profile";
 
 export default defineEventHandler(async (event) => {
   const user = await requireUser(event);

backend/server/api/me/presence-visibility.post.ts

@@ -8,6 +8,7 @@
  * Response: { presenceVisible: boolean }
  */
 import { requireUser } from "../../utils/auth";
+import { setPresenceVisible } from "../../db/profile";
 
 export default defineEventHandler(async (event) => {
   const user = await requireUser(event);

backend/server/api/presence/last-seen.get.ts

@@ -21,6 +21,7 @@
  * other profile field (feedback_anonymity_nickname.md).
  */
 import { requireUser } from "../../utils/auth";
+import { getLastSeenBatch } from "../../db/profile";
 
 const MAX_USER_IDS = 50;