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>

docs/scratchpads/ms22-agent-memory.md

@@ -0,0 +1,64 @@
+# MS22 Agent Memory Module
+
+## Objective
+
+Add per-agent key/value store: AgentMemory model + NestJS module with CRUD endpoints.
+
+## Issues
+
+- MS22-DB-002: Add AgentMemory schema model
+- MS22-API-002: Add agent-memory NestJS module
+
+## Plan
+
+1. AgentMemory model → schema.prisma (after AgentSession, line 736)
+2. Add `agentMemories AgentMemory[]` relation to Workspace model
+3. Create apps/api/src/agent-memory/ with service, controller, DTOs, specs
+4. Register in app.module.ts
+5. Migrate: `prisma migrate dev --name ms22_agent_memory`
+6. lint + build
+7. Commit
+
+## Endpoints
+
+- PUT /api/agents/:agentId/memory/:key (upsert)
+- GET /api/agents/:agentId/memory (list all)
+- GET /api/agents/:agentId/memory/:key (get one)
+- DELETE /api/agents/:agentId/memory/:key (remove)
+
+## Auth
+
+- @UseGuards(AuthGuard, WorkspaceGuard, PermissionGuard)
+- @Workspace() decorator for workspaceId
+- Permission.WORKSPACE_MEMBER for write ops
+- Permission.WORKSPACE_ANY for read ops
+
+## Schema
+
+```prisma
+model AgentMemory {
+  id          String   @id @default(uuid()) @db.Uuid
+  workspaceId String   @map("workspace_id") @db.Uuid
+  agentId     String   @map("agent_id")
+  key         String
+  value       Json
+  createdAt   DateTime @default(now()) @map("created_at") @db.Timestamptz
+  updatedAt   DateTime @updatedAt @map("updated_at") @db.Timestamptz
+
+  workspace Workspace @relation(fields: [workspaceId], references: [id], onDelete: Cascade)
+
+  @@unique([workspaceId, agentId, key])
+  @@index([workspaceId])
+  @@index([agentId])
+  @@map("agent_memories")
+}
+```
+
+## Progress
+
+- [ ] Schema
+- [ ] Module files
+- [ ] app.module.ts
+- [ ] Migration
+- [ ] lint/build
+- [ ] Commit