feat(auth): center-scoped single admin + GET /admin-email + cli

Triage channels in Guilds need to deliver every message to a single
"observer" admin user across the whole Center deployment (regardless of
on-duty / mention). This adds the data + auth surface for that.

## Schema

`users.isAdmin TINYINT DEFAULT 0` (synchronize:true auto-applies; cli
`user set-admin` enforces at-most-one in a transaction).

## CLI (subject `user`)

- `set-admin --email <e>` — clears every other admin row first, then
  marks the target. Returns `{admin: {email, userId}}`
- `clear-admin` — unsets all (returns `{cleared: N}`)
- `show-admin` — prints `{admin: {email, userId}}` or `{admin: null}`

## HTTP

`GET /auth/admin-email` (NOT @Public — requires a guild-node api key
via the existing CenterApiKeyGuard). Returns:
  - `{email: "...", userId: "..."}` if an admin exists
  - `null` (literal JSON) if no admin

Guild backends cache the result (1 day TTL per spec; with cli refresh
override on guild side).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/auth/auth.controller.ts

@@ -79,6 +79,15 @@ export class AuthController {
     return this.authService.agentLogin(String(body?.apiKey ?? ''));
   }
 
+  // Not @Public(): requires a guild node api key. Returns the single
+  // Center-scoped admin user `{email, userId}` so the calling guild can
+  // mark them as triage observers, or `null` if no admin is set.
+  @Get('admin-email')
+  getAdminEmail(@Req() req: { guildNode?: AuthedGuildNode }) {
+    if (!req.guildNode) throw new UnauthorizedException('guild node api key required');
+    return this.authService.getAdminEmail();
+  }
+
   // Not @Public(): requires a guild node api key. The guard attaches the
   // authenticated node; a node may only introspect tokens for its own
   // guild (Center C2 — prevents cross-tenant identity probing).

src/auth/auth.service.ts

@@ -204,6 +204,56 @@ export class AuthService {
     return { guilds, guildAccessTokens };
   }
 
+  // -------------------------------------------------------------------
+  // Center-scoped admin (at most one per deployment).
+  //
+  // setAdmin / clearAdmin are reachable only via cli, not HTTP — admin
+  // promotion bypasses every HTTP gate (the admin observes ALL triage
+  // traffic) so we don't want it tunneled through any token / api-key.
+  //
+  // getAdminEmail is exposed to guild backends (api-key auth) so each
+  // guild can mark the admin as a triage observer.
+  // -------------------------------------------------------------------
+
+  async getAdminEmail(): Promise<{ email: string; userId: string } | null> {
+    const admin = await this.userRepo.findOne({ where: { isAdmin: true } });
+    if (!admin) return null;
+    return { email: admin.email, userId: admin.id };
+  }
+
+  async setAdmin(email: string): Promise<{ email: string; userId: string }> {
+    const target = await this.userRepo.findOne({ where: { email } });
+    if (!target) {
+      throw new UnauthorizedException(`user ${email} not found`);
+    }
+    // Enforce at-most-one-admin: clear every other row first, then set
+    // the target. Two UPDATEs in one txn so a peer never sees two admins.
+    await this.userRepo.manager.transaction(async (txn) => {
+      await txn.update(User, {}, { isAdmin: false });
+      await txn.update(User, { id: target.id }, { isAdmin: true });
+    });
+    await this.audit.write({
+      action: 'admin.set',
+      actorId: target.id,
+      targetType: 'user',
+      targetId: target.id,
+      detail: JSON.stringify({ email: target.email }),
+    });
+    return { email: target.email, userId: target.id };
+  }
+
+  async clearAdmin(): Promise<{ cleared: number }> {
+    const res = await this.userRepo.update({ isAdmin: true }, { isAdmin: false });
+    await this.audit.write({
+      action: 'admin.clear',
+      actorId: 'cli',
+      targetType: 'user',
+      targetId: 'all',
+      detail: JSON.stringify({ cleared: res.affected ?? 0 }),
+    });
+    return { cleared: res.affected ?? 0 };
+  }
+
   async register(input: RegisterDto) {
     const exists = await this.userRepo.findOne({ where: { email: input.email } });
     if (exists) {

src/cli.ts

@@ -15,6 +15,9 @@ function printUsageAndExit(): never {
   console.error('Usage:');
   console.error('  node dist/cli.js user create --email <email> --password <password>');
   console.error('  node dist/cli.js user apikey --email <email> [--label <label>]');
+  console.error('  node dist/cli.js user set-admin --email <email>');
+  console.error('  node dist/cli.js user clear-admin');
+  console.error('  node dist/cli.js user show-admin');
   console.error('  node dist/cli.js node register --node-id <id> --name <name> --endpoint <url>');
   console.error(
     '  node dist/cli.js config oidc [--issuer <url>] [--client-id <id>] [--client-secret <s>]\n' +
@@ -52,6 +55,30 @@ async function main() {
       return;
     }
 
+    if (subject === 'user' && action === 'set-admin') {
+      const email = getArg('--email');
+      if (!email) printUsageAndExit();
+
+      const auth = app.get(AuthService);
+      const res = await auth.setAdmin(email);
+      process.stdout.write(JSON.stringify({ ok: true, admin: res }) + '\n');
+      return;
+    }
+
+    if (subject === 'user' && action === 'clear-admin') {
+      const auth = app.get(AuthService);
+      const res = await auth.clearAdmin();
+      process.stdout.write(JSON.stringify({ ok: true, ...res }) + '\n');
+      return;
+    }
+
+    if (subject === 'user' && action === 'show-admin') {
+      const auth = app.get(AuthService);
+      const res = await auth.getAdminEmail();
+      process.stdout.write(JSON.stringify({ ok: true, admin: res }) + '\n');
+      return;
+    }
+
     if (subject === 'node' && action === 'register') {
       const nodeId = getArg('--node-id');
       const name = getArg('--name');

src/entities/user.entity.ts

@@ -17,6 +17,19 @@ export class User {
   @Column({ type: 'varchar', length: 255, nullable: true })
   refreshTokenHash!: string | null;
 
+  /**
+   * Center-scoped admin flag. At most one user should have this set at a
+   * time; the cli `user set-admin` enforces single-admin by clearing all
+   * other admins before promoting the target user. Guild backends learn
+   * the current admin via `GET /admin-email`.
+   *
+   * Use: triage channels deliver every message to the admin as a silent
+   * observer (wake=false) regardless of on-duty / mention status, so a
+   * single human can audit all triage traffic.
+   */
+  @Column({ type: 'tinyint', default: 0, name: 'isAdmin' })
+  isAdmin!: boolean;
+
   @CreateDateColumn()
   createdAt!: Date;
 }