perf(ai-moderation): drop personal user-profile descriptions from context

User insight: personal profile summaries bloat the prompt (less room per
request) and add a per-user DB/Redis round-trip for little moderation signal.
Only the behavioural <user_reputation> history is kept.

- textBatchProcessor: stop fetching getUserProfile; remove <user_profiles>
  block + <user_profile_ref> from message tags. Keep <user_reputation>.
- mediaBatchProcessor + visionAnalyzer: same removal (profile fetch + ref).
- prompts/system.ts + prompts/output.ts: drop stale <user_profiles>/
  <user_profile_ref> instructions; point LLM at <user_reputation> instead.
- aiAnalyzer: gate userProfileLearner behind AI_USER_PROFILE_LEARNING_ENABLED
  (default false) — generates profiles nobody reads, pure LLM/DB waste.
- Add AI_USER_PROFILE_LEARNING_ENABLED config knob.

Net: smaller prompts (more messages fit per request), fewer DB round-trips
per sub-batch, and no background LLM calls learning unused profiles.

tsc, biome, vitest (129) all clean.

services/discord-gateway/src/modules/ai-moderation/aiAnalyzer.ts

@@ -136,9 +136,11 @@ export function startPendingAIAnalysisWorker(
   import("./cultureLearner.js")
     .then((m) => m.startCultureLearnerWorker())
     .catch(console.error);
-  import("./userProfileLearner.js")
-    .then((m) => m.startUserProfileLearnerWorker())
-    .catch(console.error);
+  if (config.AI_USER_PROFILE_LEARNING_ENABLED) {
+    import("./userProfileLearner.js")
+      .then((m) => m.startUserProfileLearnerWorker())
+      .catch(console.error);
+  }
 
   setInterval(() => {
     // [D] Periodic cache hygiene: purge expired moderation verdicts from