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/app.module.ts

@@ -27,6 +27,7 @@ import { LlmUsageModule } from "./llm-usage/llm-usage.module";
 import { BrainModule } from "./brain/brain.module";
 import { CronModule } from "./cron/cron.module";
 import { AgentTasksModule } from "./agent-tasks/agent-tasks.module";
+import { AgentMemoryModule } from "./agent-memory/agent-memory.module";
 import { ValkeyModule } from "./valkey/valkey.module";
 import { BullMqModule } from "./bullmq/bullmq.module";
 import { StitcherModule } from "./stitcher/stitcher.module";
@@ -100,6 +101,7 @@ import { RlsContextInterceptor } from "./common/interceptors/rls-context.interce
     BrainModule,
     CronModule,
     AgentTasksModule,
+    AgentMemoryModule,
     RunnerJobsModule,
     JobEventsModule,
     JobStepsModule,