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/dto/list-conversations.dto.ts

@@ -0,0 +1,33 @@
+import { IsString, IsOptional, MaxLength, IsInt, Min, Max, IsDateString } from "class-validator";
+import { Type } from "class-transformer";
+
+/**
+ * DTO for listing/filtering conversation archives
+ */
+export class ListConversationsDto {
+  @IsOptional()
+  @IsString()
+  @MaxLength(500)
+  agentId?: string;
+
+  @IsOptional()
+  @IsDateString()
+  startedAfter?: string;
+
+  @IsOptional()
+  @IsDateString()
+  startedBefore?: string;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  @Min(1)
+  page?: number;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  @Min(1)
+  @Max(100)
+  limit?: number;
+}