feat: add markdown import/export (closes #77, #78)

- Add POST /api/knowledge/import endpoint for .md and .zip files
- Add GET /api/knowledge/export endpoint with markdown/json formats
- Import parses frontmatter (title, tags, status, visibility)
- Export includes frontmatter in markdown format
- Add ImportExportActions component with drag-and-drop UI
- Add import progress dialog with success/error summary
- Add export dropdown with format selection
- Include comprehensive test suite
- Support bulk import with detailed error reporting

apps/api/src/knowledge/dto/import-export.dto.ts

@@ -0,0 +1,52 @@
+import {
+  IsString,
+  IsOptional,
+  IsEnum,
+  IsArray,
+  ArrayMinSize,
+} from "class-validator";
+
+/**
+ * Export format enum
+ */
+export enum ExportFormat {
+  MARKDOWN = "markdown",
+  JSON = "json",
+}
+
+/**
+ * DTO for export query parameters
+ */
+export class ExportQueryDto {
+  @IsOptional()
+  @IsEnum(ExportFormat, { message: "format must be either 'markdown' or 'json'" })
+  format?: ExportFormat = ExportFormat.MARKDOWN;
+
+  @IsOptional()
+  @IsArray({ message: "entryIds must be an array" })
+  @IsString({ each: true, message: "each entryId must be a string" })
+  entryIds?: string[];
+}
+
+/**
+ * Import result for a single entry
+ */
+export interface ImportResult {
+  filename: string;
+  success: boolean;
+  entryId?: string;
+  slug?: string;
+  title?: string;
+  error?: string;
+}
+
+/**
+ * Response DTO for import operation
+ */
+export interface ImportResponseDto {
+  success: boolean;
+  totalFiles: number;
+  imported: number;
+  failed: number;
+  results: ImportResult[];
+}

apps/api/src/knowledge/dto/index.ts

@@ -10,3 +10,9 @@ export {
   RecentEntriesDto,
 } from "./search-query.dto";
 export { GraphQueryDto } from "./graph-query.dto";
+export {
+  ExportQueryDto,
+  ExportFormat,
+  ImportResult,
+  ImportResponseDto,
+} from "./import-export.dto";