feat(api): add conversation archive with vector search (MS22-DB-004, MS22-API-004) (#587)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/api/src/conversation-archive/dto/search-conversation.dto.ts

@@ -0,0 +1,40 @@
+import {
+  IsString,
+  IsOptional,
+  MinLength,
+  MaxLength,
+  IsInt,
+  Min,
+  Max,
+  IsNumber,
+} from "class-validator";
+import { Type } from "class-transformer";
+
+/**
+ * DTO for semantic search across conversation archives
+ */
+export class SearchConversationDto {
+  @IsString()
+  @MinLength(1)
+  @MaxLength(1000)
+  query!: string;
+
+  @IsOptional()
+  @IsString()
+  @MaxLength(500)
+  agentId?: string;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  @Min(1)
+  @Max(100)
+  limit?: number;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsNumber()
+  @Min(0)
+  @Max(1)
+  similarityThreshold?: number;
+}