feat: Add organization name and scheduler refresh interval settings

- Superadmin-only organization name setting displayed in dashboard header
- Advanced Options tab with configurable scheduler refresh interval (0 = disabled)
- Make system settings GET endpoint public for frontend reads
- Scheduler reads refresh_seconds from DB dynamically each loop
- Seed default system settings in init_defaults.py

server/routes/system_settings.py

@@ -5,7 +5,7 @@ Provides key-value storage for system-wide configuration.
 from flask import Blueprint, jsonify, request
 from server.database import Session
 from models.models import SystemSetting
-from server.permissions import admin_or_higher
+from server.permissions import admin_or_higher, superadmin_only
 from sqlalchemy.exc import SQLAlchemyError
 
 system_settings_bp = Blueprint('system_settings', __name__, url_prefix='/api/system-settings')
@@ -31,11 +31,10 @@ def get_all_settings():
 
 
 @system_settings_bp.route('/<key>', methods=['GET'])
-@admin_or_higher
 def get_setting(key):
     """
     Get a specific system setting by key.
-    Admin+ only.
+    Public endpoint - settings are read-only configuration.
     """
     session = Session()
     try:
@@ -265,3 +264,66 @@ def update_holiday_banner_setting():
     finally:
         session.close()
 
+
+@system_settings_bp.route('/organization-name', methods=['GET'])
+def get_organization_name():
+    """
+    Get organization name.
+    Public endpoint - header needs this.
+    """
+    session = Session()
+    try:
+        setting = session.query(SystemSetting).filter_by(key='organization_name').first()
+        name = setting.value if setting and setting.value else ''
+        
+        return jsonify({'name': name}), 200
+    except SQLAlchemyError as e:
+        return jsonify({'error': str(e)}), 500
+    finally:
+        session.close()
+
+
+@system_settings_bp.route('/organization-name', methods=['POST'])
+@superadmin_only
+def update_organization_name():
+    """
+    Update organization name.
+    Superadmin only.
+    
+    Request body:
+    {
+        "name": "Meine Organisation"
+    }
+    """
+    session = Session()
+    try:
+        data = request.get_json()
+        if not data:
+            return jsonify({'error': 'No data provided'}), 400
+        
+        name = data.get('name', '')
+        
+        # Update or create setting
+        setting = session.query(SystemSetting).filter_by(key='organization_name').first()
+        if setting:
+            setting.value = name
+        else:
+            setting = SystemSetting(
+                key='organization_name',
+                value=name,
+                description='Name der Organisation (wird im Header angezeigt)'
+            )
+            session.add(setting)
+        
+        session.commit()
+        
+        return jsonify({
+            'name': name,
+            'message': 'Organization name updated successfully'
+        }), 200
+    except SQLAlchemyError as e:
+        session.rollback()
+        return jsonify({'error': str(e)}), 500
+    finally:
+        session.close()
+