feat(api): add conversation archive with vector search (MS22-DB-004, MS22-API-004)

- Add ConversationArchive Prisma model with pgvector(1536) embedding field
- Migration: 20260228000000_ms22_conversation_archive
- NestJS module at apps/api/src/conversation-archive/ with service, controller, DTOs, spec
- POST /api/conversations/ingest — ingest session logs, auto-embed via EmbeddingService
- POST /api/conversations/search — vector similarity search with agentId filter
- GET  /api/conversations — paginated list with agentId + date range filters
- GET  /api/conversations/:id — fetch full conversation including messages
- Register ConversationArchiveModule in app.module.ts
- 8 unit tests, all passing (vitest)

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

apps/api/src/conversation-archive/conversation-archive.module.ts

@@ -0,0 +1,14 @@
+import { Module } from "@nestjs/common";
+import { PrismaModule } from "../prisma/prisma.module";
+import { AuthModule } from "../auth/auth.module";
+import { KnowledgeModule } from "../knowledge/knowledge.module";
+import { ConversationArchiveService } from "./conversation-archive.service";
+import { ConversationArchiveController } from "./conversation-archive.controller";
+
+@Module({
+  imports: [PrismaModule, AuthModule, KnowledgeModule],
+  controllers: [ConversationArchiveController],
+  providers: [ConversationArchiveService],
+  exports: [ConversationArchiveService],
+})
+export class ConversationArchiveModule {}