feat(api): agent bearer auth middleware

Add lib/api/middleware/agent_auth.js: agentOrOwner accepts the owner
token (kind=user actor) or a hashed agent token (kind=agent actor
carrying capabilities + scopes). /api router now mounts this in place
of ownerOnly so agent tokens become first-class.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/api/middleware/agent_auth.js

@@ -0,0 +1,32 @@
+import * as agents from '../../db/repos/agents.js';
+
+export async function agentOrOwner(req, res, next) {
+  const expectedOwner = process.env.OWNER_TOKEN;
+  if (!expectedOwner) {
+    return res.status(500).json({
+      error: { code: 'no_owner_token', message: 'OWNER_TOKEN not configured' }
+    });
+  }
+  const auth = req.headers.authorization || '';
+  const [scheme, token] = auth.split(' ');
+  if (scheme !== 'Bearer' || !token) {
+    return res.status(401).json({ error: { code: 'unauthorized', message: 'missing bearer token' } });
+  }
+  if (token === expectedOwner) {
+    req.actor = { kind: 'user', id: null };
+    return next();
+  }
+  try {
+    const agent = await agents.verifyToken(token);
+    if (!agent) {
+      return res.status(401).json({ error: { code: 'unauthorized', message: 'invalid token' } });
+    }
+    req.actor = {
+      kind: 'agent',
+      id: agent.id,
+      capabilities: agent.capabilities || {},
+      scopes: agent.scopes || {}
+    };
+    next();
+  } catch (e) { next(e); }
+}