feat(frontend): add thumbnailKey and thumbnailGeneratedAt to Document type

Mirrors the backend Document entity's new optional fields. Both are
optional (no @Schema requiredMode on the backend side), so legacy
documents without thumbnails stay valid.

Refs #307

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/generated/api.ts

@@ -1383,6 +1383,9 @@ export interface components {
             filePath?: string;
             contentType?: string;
             fileHash?: string;
+            thumbnailKey?: string;
+            /** Format: date-time */
+            thumbnailGeneratedAt?: string;
             originalFilename: string;
             /** @enum {string} */
             status: "PLACEHOLDER" | "UPLOADED" | "TRANSCRIBED" | "REVIEWED" | "ARCHIVED";