feat: Initialize frontend with React, Vite, and Tailwind CSS

- Set up main entry point for React application.
- Create About, Home, NotFound, Privacy, and Terms pages with SEO support.
- Implement API service for file uploads and task management.
- Add global styles using Tailwind CSS.
- Create utility functions for SEO and text processing.
- Configure Vite for development and production builds.
- Set up Nginx configuration for serving frontend and backend.
- Add scripts for cleanup of expired files and sitemap generation.
- Implement deployment script for production environment.

backend/app/routes/download.py

@@ -0,0 +1,35 @@
+"""Local file download route — used when S3 is not configured."""
+import os
+
+from flask import Blueprint, send_file, abort, request, current_app
+
+download_bp = Blueprint("download", __name__)
+
+
+@download_bp.route("/<task_id>/<filename>", methods=["GET"])
+def download_file(task_id: str, filename: str):
+    """
+    Serve a processed file from local filesystem.
+
+    Only active in development (when S3 is not configured).
+    """
+    # Security: sanitize inputs
+    # Only allow UUID-style task IDs and safe filenames
+    if ".." in task_id or "/" in task_id or "\\" in task_id:
+        abort(400, "Invalid task ID.")
+    if ".." in filename or "/" in filename or "\\" in filename:
+        abort(400, "Invalid filename.")
+
+    output_dir = current_app.config["OUTPUT_FOLDER"]
+    file_path = os.path.join(output_dir, task_id, filename)
+
+    if not os.path.isfile(file_path):
+        abort(404, "File not found or expired.")
+
+    download_name = request.args.get("name", filename)
+
+    return send_file(
+        file_path,
+        as_attachment=True,
+        download_name=download_name,
+    )