feat(guild): slash-command registry (sync + list API)

Guild-global slash-command catalog (one row per node guild). The
OpenClaw plugin PUTs the native-command specs (same data Discord
registers as slash commands); the frontend GETs it for / autocomplete.

- GuildCommand entity (guild_id unique, commands json, updatedAt)
- PUT /api/commands  -> idempotent full replace (any authed agent/user)
- GET /api/commands  -> { commands, updatedAt } (authed)
- stored verbatim (NativeCommandSpec-shaped); execution path unchanged:
  a /<cmd> message is delivered as a normal message -> plugin ->
  OpenClaw command system (only /no-reply, /force-proceed stay
  server-intercepted).

Verified: PUT->{ok,count}, GET round-trips args/choices, no-auth->401.

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

src/commands/commands.service.ts

@@ -0,0 +1,39 @@
+import { Injectable } from '@nestjs/common';
+import { InjectRepository } from '@nestjs/typeorm';
+import { Repository } from 'typeorm';
+import { GuildCommand } from '../entities/guild-command.entity.js';
+
+// This node's guild id (one guild per node).
+function guildId(): string {
+  return process.env.FABRIC_BACKEND_GUILD_NODE_ID ?? 'guild';
+}
+
+@Injectable()
+export class CommandsService {
+  constructor(
+    @InjectRepository(GuildCommand)
+    private readonly repo: Repository<GuildCommand>,
+  ) {}
+
+  // Replace the whole guild-global slash-command catalog (idempotent;
+  // the plugin re-PUTs the full set on every gateway start).
+  async sync(commands: unknown[]): Promise<{ status: string; count: number }> {
+    const gid = guildId();
+    let row = await this.repo.findOne({ where: { guildId: gid } });
+    if (row) {
+      row.commands = commands;
+    } else {
+      row = this.repo.create({ guildId: gid, commands });
+    }
+    await this.repo.save(row);
+    return { status: 'ok', count: commands.length };
+  }
+
+  async list(): Promise<{ commands: unknown[]; updatedAt: string | null }> {
+    const row = await this.repo.findOne({ where: { guildId: guildId() } });
+    return {
+      commands: row?.commands ?? [],
+      updatedAt: row?.updatedAt ? row.updatedAt.toISOString() : null,
+    };
+  }
+}