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/timestamp.py

@@ -0,0 +1,46 @@
+from flask import Blueprint, request, jsonify
+from datetime import datetime, timezone
+from util.logger import logger
+from auth.token import verify_token
+
+timestamp_blueprint = Blueprint('timestamp_tool', __name__)
+
+_DATE_FORMATS = [
+    "%Y-%m-%dT%H:%M:%S",
+    "%Y-%m-%d %H:%M:%S",
+    "%Y-%m-%d",
+    "%d.%m.%Y %H:%M:%S",
+    "%d.%m.%Y",
+]
+
+
+@timestamp_blueprint.route('/api/timestamp/convert', methods=['POST'])
+def convert_timestamp():
+    user = verify_token()
+    if not user:
+        return jsonify({"message": "Nicht autorisiert"}), 401
+    try:
+        data = request.get_json()
+        value = data.get("value", "").strip()
+        direction = data.get("direction", "unix_to_date")
+
+        if direction == "unix_to_date":
+            ts = float(value)
+            dt_utc = datetime.fromtimestamp(ts, tz=timezone.utc)
+            return jsonify({"utc": dt_utc.isoformat(), "unix": int(ts)})
+
+        dt = None
+        for fmt in _DATE_FORMATS:
+            try:
+                dt = datetime.strptime(value, fmt).replace(tzinfo=timezone.utc)
+                break
+            except ValueError:
+                continue
+        if dt is None:
+            return jsonify({"message": "Ungültiges Datumsformat"}), 400
+
+        logger.info(f"Timestamp konvertiert von {user['username']}")
+        return jsonify({"unix": int(dt.timestamp()), "utc": dt.isoformat()})
+    except Exception as e:
+        logger.error(f"Fehler Timestamp: {e}")
+        return jsonify({"message": "Ungültiger Wert"}), 400