refactor(guild-discovery): drop serviceEndpoint (no longer needed)

Pairs with Dialectic.Backend@5cf4302 which removes the backend-driven
broadcast that was the only consumer of serviceEndpoint. With agent-
driven recruitment broadcasts via fabric-send-message, the
service-to-service URL distinction goes away (agents use the regular
guild endpoint).

Removed:
  - GuildNode.serviceEndpoint column (TypeORM will drop on next sync)
  - GET /api/auth/me/guilds + /api/nodes response fields
  - NodeAdminService.setServiceEndpoint()
  - cli 'node set-service-endpoint' subcommand

Kept:
  - GuildNode.purpose (used by fabric-guild-list for intent-based
    channel discovery — still wanted)

src/nodes/node-admin.service.ts

@@ -56,29 +56,6 @@ export class NodeAdminService {
     };
   }
 
-  // Admin-only via cli: set the service-to-service endpoint for a guild
-  // node. This is the URL that another *service in the same deployment*
-  // (e.g. dialectic-backend on compose) uses to reach the guild — NOT
-  // the public client-facing URL. Pass empty string to clear.
-  async setServiceEndpoint(nodeId: string, serviceEndpoint: string) {
-    const node = await this.nodeRepo.findOne({ where: { nodeId } });
-    if (!node) throw new NotFoundException(`node ${nodeId} not found`);
-    const trimmed = String(serviceEndpoint ?? '').trim();
-    node.serviceEndpoint = trimmed === '' ? null : trimmed;
-    const saved = await this.nodeRepo.save(node);
-    await this.audit.write({
-      action: 'node.set_service_endpoint',
-      targetType: 'node',
-      targetId: saved.nodeId,
-      detail: JSON.stringify({ serviceEndpoint: saved.serviceEndpoint, via: 'cli' }),
-    });
-    return {
-      nodeId: saved.nodeId,
-      name: saved.name,
-      serviceEndpoint: saved.serviceEndpoint,
-    };
-  }
-
   // Admin-only via cli (never HTTP): set the free-form purpose string on
   // a guild node. Pass an empty string to clear it (null).
   async setPurpose(nodeId: string, purpose: string) {