feat(ai-moderation): enrich analysis context with recency, repetition, user history and channel topic

- <message> targets now carry time (ISO), repetitions (N identical short texts = spam signal), bot and edited flags; escape id/user XML
- rich <user_reputation>: total_infractions, clean_streak, last_offense_days_ago, repeat_offender (7-day window)
- <user_history> with last flagged messages for repeat offenders (wires dead getUserRecentInfractions)
- <user_profile as_of> staleness signal; <location_context topic> from captured channel topic
- prompt framing + output instructions teach the LLM to use the new signals without treating history as proof
- tests: contextEnrichment.test.ts (13) + topic cases in conversationContext.test.ts

services/frontend/src/lib/types/message.ts

@@ -71,6 +71,9 @@ export interface ChannelRef {
   channelName?: string | null;
   threadId?: string | null;
   threadName?: string | null;
+  /** Channel topic (captured in gateway metadata.channel.topic). */
+  topic?: string | null;
+  nsfw?: boolean;
 }
 
 export interface ReferenceInfo {