Add 6 new tools: Hasher, Base64, JWT Decoder, Password Gen, Timestamp, Text Diff

- backend/tools/hasher.py: POST /api/hash/sha256 and /api/hash/bcrypt (bcrypt added to requirements)
- backend/tools/base64tool.py: POST /api/base64/encode and /api/base64/decode
- backend/tools/jwtdecoder.py: POST /api/jwt/decode (signature verification disabled)
- backend/tools/passwordgen.py: POST /api/password/generate with charset and length options
- backend/tools/timestamp.py: POST /api/timestamp/convert (unix<->date, ISO 8601 + German format)
- backend/tools/textdiff.py: POST /api/text/diff returning structured added/removed/unchanged lines
- All blueprints registered in app.py and tools/__init__.py
- React components with copy button, dark/light mode support via CSS variables
- ToolOverview rebuilt as card grid; App.jsx routes added for all tools

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

backend/tools/textdiff.py

@@ -0,0 +1,37 @@
+from flask import Blueprint, request, jsonify
+import difflib
+from util.logger import logger
+from auth.token import verify_token
+
+textdiff_blueprint = Blueprint('textdiff_tool', __name__)
+
+
+@textdiff_blueprint.route('/api/text/diff', methods=['POST'])
+def text_diff():
+    user = verify_token()
+    if not user:
+        return jsonify({"message": "Nicht autorisiert"}), 401
+    try:
+        data = request.get_json()
+        text1 = data.get("text1", "")
+        text2 = data.get("text2", "")
+
+        lines1 = text1.splitlines(keepends=True)
+        lines2 = text2.splitlines(keepends=True)
+
+        result = []
+        for line in difflib.unified_diff(lines1, lines2, lineterm=''):
+            if line.startswith('+++') or line.startswith('---') or line.startswith('@@'):
+                continue
+            if line.startswith('+'):
+                result.append({"type": "added", "text": line[1:]})
+            elif line.startswith('-'):
+                result.append({"type": "removed", "text": line[1:]})
+            else:
+                result.append({"type": "unchanged", "text": line[1:] if line.startswith(' ') else line})
+
+        logger.info(f"Text-Diff erstellt von {user['username']}")
+        return jsonify({"diff": result})
+    except Exception as e:
+        logger.error(f"Fehler Text-Diff: {e}")
+        return jsonify({"message": "Fehler beim Vergleich"}), 500