feat(threads): persist autoArchiveAt in thread meta rows

Store scheduled auto-archive timestamps when creating threads with
autoArchiveMinutes so partition heal can archive expired threads (Phase 679).

Co-authored-by: Cursor <[email protected]>

index.js

@@ -141,6 +141,7 @@ class PearcordGuild extends EventEmitter {
       archived: meta.archived === true,
       createdAt: meta.createdAt || now()
     }
+    if (meta.autoArchiveAt != null) row.autoArchiveAt = Number(meta.autoArchiveAt) || 0
     await this.db.insert(COLLECTIONS.THREAD_META, row)
     return row
   }
@@ -1296,7 +1297,7 @@ class PearcordGuild extends EventEmitter {
     return merged
   }
 
-  async createThread ({ parentChannelId, rootMessageId, name }) {
+  async createThread ({ parentChannelId, rootMessageId, name, autoArchiveMinutes = 0 }) {
     if (!this.guild) throw new Error('no active guild')
     if (!parentChannelId || !rootMessageId) {
       throw new Error('parentChannelId and rootMessageId required')
@@ -1328,6 +1329,14 @@ class PearcordGuild extends EventEmitter {
       parentChannelId,
       { rootMessageId, archived: false }
     )
+    if (autoArchiveMinutes > 0 && channel?.id) {
+      await this._upsertThreadMeta({
+        guildId: this.guild.id,
+        channelId: channel.id,
+        rootMessageId,
+        autoArchiveAt: Date.now() + autoArchiveMinutes * 60 * 1000
+      }).catch(() => {})
+    }
     this.emit('channel', channel)
     return channel
   }