feat(api): add API documentation and ShareX integration

- Add an API documentation page with curl and ShareX examples.
- Implement a dynamic ShareX configuration endpoint (`/api/v1/sharex/warpbox-anonymous.sxcu`) that generates a `.sxcu` file pre-configured with the instance's base URL.
- Update anonymous uploads to return a private management link (`manageUrl`) and a deletion link (`deleteUrl`) in JSON responses.
- Update README with details on Stage 3 Anonymous Integrations.
- Add styling for the new API documentation view and management details.

backend/libs/jobs/thumbnails.go

@@ -23,6 +23,25 @@ type thumbnailJobResult struct {
 	Failed    int
 }
 
+func GenerateThumbnailsForBoxAsync(uploadService *services.UploadService, logger *slog.Logger, boxID string) {
+	go func() {
+		box, err := uploadService.GetBox(boxID)
+		if err != nil {
+			logger.Warn("thumbnail box lookup failed", "source", "thumbnail", "severity", "warn", "code", 4204, "box_id", boxID, "error", err.Error())
+			return
+		}
+
+		result, err := generateMissingThumbnailsForBox(uploadService, logger, box)
+		if err != nil {
+			logger.Warn("thumbnail one-shot job failed", "source", "thumbnail", "severity", "warn", "code", 4205, "box_id", boxID, "error", err.Error())
+			return
+		}
+		if result.Generated > 0 || result.Failed > 0 {
+			logger.Info("thumbnail one-shot job complete", "source", "thumbnail", "severity", "user_activity", "code", 2205, "box_id", boxID, "generated", result.Generated, "failed", result.Failed)
+		}
+	}()
+}
+
 func newThumbnailsJob(cfg config.Config, logger *slog.Logger, uploadService *services.UploadService) job {
 	return job{
 		name:     "thumbnail",
@@ -54,40 +73,56 @@ func generateMissingThumbnails(uploadService *services.UploadService, logger *sl
 			continue
 		}
 
-		changed := false
-		for i := range box.Files {
-			file := &box.Files[i]
-			if file.Thumbnail != "" || !needsThumbnail(*file) {
-				continue
-			}
-			result.Scanned++
-
-			thumbnail, err := generateThumbnail(uploadService, box, *file)
-			if err != nil {
-				logger.Warn("thumbnail generation failed", "source", "thumbnail", "severity", "warn", "code", 4101, "file_id", file.ID, "error", err.Error())
-				result.Failed++
-				continue
-			}
-			if thumbnail == "" {
-				result.Failed++
-				continue
-			}
-
-			file.Thumbnail = thumbnail
-			changed = true
-			result.Generated++
-		}
-
-		if changed {
-			if err := uploadService.SaveBox(box); err != nil {
-				return result, err
-			}
+		boxResult, err := generateMissingThumbnailsForBox(uploadService, logger, box)
+		result.Scanned += boxResult.Scanned
+		result.Generated += boxResult.Generated
+		result.Failed += boxResult.Failed
+		if err != nil {
+			return result, err
 		}
 	}
 
 	return result, nil
 }
 
+func generateMissingThumbnailsForBox(uploadService *services.UploadService, logger *slog.Logger, box services.Box) (thumbnailJobResult, error) {
+	var result thumbnailJobResult
+	if !box.ExpiresAt.After(time.Now().UTC()) {
+		return result, nil
+	}
+
+	changed := false
+	for i := range box.Files {
+		file := &box.Files[i]
+		if file.Thumbnail != "" || !needsThumbnail(*file) {
+			continue
+		}
+		result.Scanned++
+
+		thumbnail, err := generateThumbnail(uploadService, box, *file)
+		if err != nil {
+			logger.Warn("thumbnail generation failed", "source", "thumbnail", "severity", "warn", "code", 4101, "file_id", file.ID, "error", err.Error())
+			result.Failed++
+			continue
+		}
+		if thumbnail == "" {
+			result.Failed++
+			continue
+		}
+
+		file.Thumbnail = thumbnail
+		changed = true
+		result.Generated++
+	}
+
+	if changed {
+		if err := uploadService.SaveBox(box); err != nil {
+			return result, err
+		}
+	}
+	return result, nil
+}
+
 func needsThumbnail(file services.File) bool {
 	return file.PreviewKind == "image" || file.PreviewKind == "video"
 }