feat(api): add agent memory module (MS22-DB-002, MS22-API-002)

- Add AgentMemory model to schema.prisma with workspaceId/agentId/key/value
  and @@unique([workspaceId, agentId, key]) constraint
- Add Workspace.agentMemories relation
- Add migration 20260228000000_ms22_agent_memory
- Add AgentMemoryModule with service, controller, DTOs, and unit tests
- Endpoints: PUT/GET/GET/:key/DELETE on /api/agents/:agentId/memory/:key
- Register AgentMemoryModule in app.module.ts
- 10 unit tests passing (service + controller)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/src/agent-memory/agent-memory.module.ts

@@ -0,0 +1,13 @@
+import { Module } from "@nestjs/common";
+import { AgentMemoryController } from "./agent-memory.controller";
+import { AgentMemoryService } from "./agent-memory.service";
+import { PrismaModule } from "../prisma/prisma.module";
+import { AuthModule } from "../auth/auth.module";
+
+@Module({
+  imports: [PrismaModule, AuthModule],
+  controllers: [AgentMemoryController],
+  providers: [AgentMemoryService],
+  exports: [AgentMemoryService],
+})
+export class AgentMemoryModule {}