feat(guild): required channel x_type enum

Channel.x_type enum(general|work|report|discuss|triage|custom); required
and validated on channel creation (400 if missing/invalid).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/entities/channel.entity.ts

@@ -13,6 +13,13 @@ export class Channel {
   @Column({ type: 'varchar', length: 120 })
   name!: string;
 
+  @Column({
+    name: 'x_type',
+    type: 'enum',
+    enum: ['general', 'work', 'report', 'discuss', 'triage', 'custom'],
+  })
+  xType!: 'general' | 'work' | 'report' | 'discuss' | 'triage' | 'custom';
+
   @Column({ type: 'varchar', length: 16, default: 'text' })
   kind!: 'text' | 'announcement';