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/discord-gateway/src/modules/message-capture/messageMetadata.ts

@@ -9,6 +9,10 @@ export interface MessageLocation {
   threadId: string | null;
   threadName: string | null;
   channelName: string | null;
+  /** Channel topic (resmi/deskripsi channel) — strong context for judging
+   *  whether a message fits the channel's purpose. Guarded: some channel
+   *  types (threads on older API builds) expose no topic. */
+  topic?: string | null;
   nsfw?: boolean;
   nsfwLevel?: string | null;
   ageRestricted?: boolean;
@@ -107,12 +111,17 @@ export function getMessageLocation(message: Message): MessageLocation {
     nsfw?: boolean;
     nsfwLevel?: string | null;
   };
+  const topic =
+    "topic" in channel && typeof channel.topic === "string"
+      ? channel.topic
+      : null;
   if (!channel.isThread?.()) {
     return {
       channelId: message.channelId,
       threadId: null,
       threadName: null,
       channelName: "name" in channel ? channel.name : null,
+      topic,
       nsfw:
         typeof safetyChannel.nsfw === "boolean"
           ? safetyChannel.nsfw
@@ -133,6 +142,7 @@ export function getMessageLocation(message: Message): MessageLocation {
     threadId: channel.id,
     threadName: channel.name,
     channelName: channel.parent?.name ?? null,
+    topic,
     nsfw:
       typeof safetyChannel.nsfw === "boolean" ? safetyChannel.nsfw : undefined,
     nsfwLevel: