feat: detect reply/forward/crosspost in message capture + inject into AI moderation

- Add is_reply, is_forward, is_crosspost, reference_message_id,
  reference_channel_id, reference_guild_id columns to messages table
- Update MessageRecord type with reference fields
- Extract reply/forward/crosspost from Discord message type/flags
- Track reference.type (DEFAULT=reply, FORWARD) and CROSSPOSTED flag
- Inject <reference> XML with parent content into LLM moderation prompt
- Add reply/forward/crosspost rules to moderation prompt rules
- Format context messages with [reply_to], [forward_from], [crosspost]
- Add migration 0009

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

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

@@ -81,7 +81,9 @@ export interface RichMessageMetadata {
     messageId: string | null;
     channelId: string | null;
     guildId: string | null;
+    type: string | null;
   } | null;
+  isCrosspost: boolean;
 }
 
 export function getMessageLocation(message: Message): MessageLocation {
@@ -235,8 +237,10 @@ export function getMessageMetadata(message: Message): RichMessageMetadata {
           messageId: message.reference.messageId ?? null,
           channelId: message.reference.channelId ?? null,
           guildId: message.reference.guildId ?? null,
+          type: (message.reference.type as unknown as string | undefined) ?? null,
         }
       : null,
+    isCrosspost: message.flags?.has(1 << 1) ?? false,
   };
 }
 
@@ -258,6 +262,7 @@ export function parseRichMessageMetadata(
       member: (parsed.member ?? null) as RichMessageMetadata["member"],
       channel: parsed.channel as RichMessageMetadata["channel"],
       reference: (parsed.reference ?? null) as RichMessageMetadata["reference"],
+      isCrosspost: Boolean(parsed.isCrosspost),
     };
   } catch {
     return null;