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/colorconverter.py

@@ -0,0 +1,88 @@
+from flask import Blueprint, request, jsonify
+import colorsys
+import re
+from util.logger import logger
+from auth.token import verify_token
+
+color_blueprint = Blueprint('color_tool', __name__)
+
+
+def hex_to_rgb(hex_str):
+    hex_str = hex_str.strip().lstrip('#')
+    if len(hex_str) == 3:
+        hex_str = ''.join(c * 2 for c in hex_str)
+    if len(hex_str) != 6:
+        raise ValueError("Ungültiger HEX-Wert")
+    return int(hex_str[0:2], 16), int(hex_str[2:4], 16), int(hex_str[4:6], 16)
+
+
+def rgb_to_hex(r, g, b):
+    return f"#{r:02x}{g:02x}{b:02x}"
+
+
+def rgb_to_hsl(r, g, b):
+    # colorsys uses HLS order (hue, lightness, saturation)
+    h, l, s = colorsys.rgb_to_hls(r / 255, g / 255, b / 255)
+    return round(h * 360), round(s * 100), round(l * 100)
+
+
+def hsl_to_rgb(h, s, l):
+    # CSS HSL: hue 0-360, saturation 0-100, lightness 0-100
+    r, g, b = colorsys.hls_to_rgb(h / 360, l / 100, s / 100)
+    return round(r * 255), round(g * 255), round(b * 255)
+
+
+def parse_rgb(value):
+    nums = re.findall(r'\d+', value)
+    if len(nums) < 3:
+        raise ValueError("Ungültiger RGB-Wert")
+    r, g, b = int(nums[0]), int(nums[1]), int(nums[2])
+    if not all(0 <= x <= 255 for x in (r, g, b)):
+        raise ValueError("RGB-Werte müssen zwischen 0 und 255 liegen")
+    return r, g, b
+
+
+def parse_hsl(value):
+    nums = re.findall(r'[\d.]+', value)
+    if len(nums) < 3:
+        raise ValueError("Ungültiger HSL-Wert")
+    h, s, l = float(nums[0]), float(nums[1]), float(nums[2])
+    if not (0 <= h <= 360 and 0 <= s <= 100 and 0 <= l <= 100):
+        raise ValueError("HSL-Werte außerhalb des gültigen Bereichs")
+    return h, s, l
+
+
+@color_blueprint.route('/api/color/convert', methods=['POST'])
+def convert_color():
+    user = verify_token()
+    if not user:
+        return jsonify({"message": "Nicht autorisiert"}), 401
+    try:
+        data = request.get_json(silent=True) or {}
+        value = data.get("value", "").strip()
+        from_format = data.get("from_format", "hex").lower()
+
+        if from_format == "hex":
+            r, g, b = hex_to_rgb(value)
+        elif from_format == "rgb":
+            r, g, b = parse_rgb(value)
+        elif from_format == "hsl":
+            h, s, l = parse_hsl(value)
+            r, g, b = hsl_to_rgb(h, s, l)
+        else:
+            return jsonify({"message": "Unbekanntes Format"}), 400
+
+        hex_val = rgb_to_hex(r, g, b)
+        hue, sat, lig = rgb_to_hsl(r, g, b)
+
+        logger.info(f"Farbe konvertiert von {user['username']}")
+        return jsonify({
+            "hex": hex_val,
+            "rgb": f"rgb({r}, {g}, {b})",
+            "hsl": f"hsl({hue}, {sat}%, {lig}%)",
+        })
+    except ValueError as e:
+        return jsonify({"message": str(e)}), 400
+    except Exception as e:
+        logger.error(f"Fehler Farbkonverter: {e}")
+        return jsonify({"message": "Fehler bei der Konvertierung"}), 500