feat(security): Yerin security-agent toolset (read-only)

New securityRegistry (separate from companionRegistry) with two read-only,
secret-free tools for the Yerin security agent:
- audit_log: query the redacted audit trail by actor_kind/actor_id
- agent_inventory: list agents + capabilities/scopes (explicit projection,
  never SELECT *, no token material)

Follows the existing createRegistry() pattern. Design + wiring roadmap in
docs/yerin-security-agent.md. Not yet seeded/exposed over MCP (left for review).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/ai/agent/tools/security/index.js

@@ -0,0 +1,11 @@
+import { createRegistry } from '../../registry.js';
+import { auditLogTool } from './audit_log.js';
+import { agentInventoryTool } from './agent_inventory.js';
+
+// Yerin's security toolset — read-only observability, kept in its own registry
+// so the security agent gets security tools (not Dross's propose_change). A
+// future MCP server can expose this registry the same way companion-stdio.js
+// exposes companionRegistry. Roadmap for further tools: see docs/yerin-security-agent.md
+export const securityRegistry = createRegistry();
+securityRegistry.registerTool(auditLogTool);
+securityRegistry.registerTool(agentInventoryTool);