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/drizzle/migrations/0009_add_reply_forward_crosspost.sql

@@ -0,0 +1,7 @@
+ALTER TABLE messages
+  ADD COLUMN IF NOT EXISTS is_reply boolean,
+  ADD COLUMN IF NOT EXISTS is_forward boolean,
+  ADD COLUMN IF NOT EXISTS is_crosspost boolean,
+  ADD COLUMN IF NOT EXISTS reference_message_id text,
+  ADD COLUMN IF NOT EXISTS reference_channel_id text,
+  ADD COLUMN IF NOT EXISTS reference_guild_id text;

services/discord-gateway/drizzle/migrations/meta/_journal.json

@@ -64,6 +64,13 @@
       "when": 1781270000000,
       "tag": "0008_add_user_profiles_table",
       "breakpoints": true
+    },
+    {
+      "idx": 9,
+      "version": "7",
+      "when": 1781316000000,
+      "tag": "0009_add_reply_forward_crosspost",
+      "breakpoints": true
     }
   ]
 }