Add 5 new tools: QR-Code, Markdown, Color Converter, JSON Formatter, Regex Tester

- backend/tools/qrcode_gen.py: POST /api/qrcode/generate, returns base64 PNG (qrcode[pil])
- backend/tools/markdown_tool.py: POST /api/markdown/render, extensions: tables/fenced_code/nl2br
- backend/tools/colorconverter.py: POST /api/color/convert, HEX/RGB/HSL via colorsys (no deps)
- backend/tools/jsonformatter.py: POST /api/json/format, returns formatted JSON with line/col errors
- backend/tools/regextester.py: POST /api/regex/test, flags i/m/s, returns matches with positions
- QrCodeTool.jsx: generate + download PNG button
- MarkdownTool.jsx: split editor/preview, debounce 500ms, white preview bg
- ColorConverterTool.jsx: color swatch preview, per-format copy buttons
- JsonFormatterTool.jsx: indent toggle 2/4, pre result box with copy
- RegexTesterTool.jsx: debounce 400ms, yellow match highlighting, flag checkboxes
- All blueprints registered in app.py; qrcode[pil] + markdown added to requirements.txt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/tools/jsonformatter.py

@@ -0,0 +1,26 @@
+from flask import Blueprint, request, jsonify
+import json
+from util.logger import logger
+from auth.token import verify_token
+
+json_formatter_blueprint = Blueprint('json_formatter_tool', __name__)
+
+
+@json_formatter_blueprint.route('/api/json/format', methods=['POST'])
+def format_json():
+    user = verify_token()
+    if not user:
+        return jsonify({"message": "Nicht autorisiert"}), 401
+    try:
+        data = request.get_json(silent=True) or {}
+        text = data.get("text", "")
+        indent = int(data.get("indent", 2))
+
+        parsed = json.loads(text)
+        formatted = json.dumps(parsed, indent=indent, ensure_ascii=False)
+        return jsonify({"result": formatted})
+    except json.JSONDecodeError as e:
+        return jsonify({"message": f"JSON-Fehler in Zeile {e.lineno}, Spalte {e.colno}: {e.msg}"}), 400
+    except Exception as e:
+        logger.error(f"Fehler JSON-Formatter: {e}")
+        return jsonify({"message": "Fehler beim Formatieren"}), 500