Add admin payment settings UI with complete API endpoints

- Created admin_payment_settings.html template with system status dashboard
- Added route /dashboard/admin/payment-settings in main.py
- Implemented GET /api/admin/payment-system/status endpoint (master keys, balances, pending/failed payments)
- Implemented GET /api/admin/payment-system/config endpoint (all payment config)
- Implemented PUT /api/admin/payment-system/config/* endpoints:
  - /price-sources - Configure crypto price sources
  - /blockchain - Configure blockchain monitoring
  - /email - Configure email notifications
  - /consolidation - Configure wallet consolidation
- Added Payment Settings link to admin navigation menu in base.html
- Maintained backward compatibility with legacy POST endpoints

templates/base.html

@@ -507,6 +507,7 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
             <a href="{{ url_for(request, '/dashboard/users') }}" {% if '/users' in request.path %}class="active"{% endif %}>Users</a>
             <a href="{{ url_for(request, '/dashboard/settings') }}" {% if '/settings' in request.path %}class="active"{% endif %}>Settings</a>
             <a href="{{ url_for(request, '/dashboard/admin/tiers') }}" {% if '/admin/tiers' in request.path %}class="active"{% endif %}>Tiers</a>
+            <a href="{{ url_for(request, '/dashboard/admin/payment-settings') }}" {% if '/admin/payment-settings' in request.path %}class="active"{% endif %}>Payment Settings</a>
             {% endif %}
             {% if show_upgrade_button %}
             <a href="{{ url_for(request, '/dashboard/pricing') }}" class="upgrade-button rainbow-text">✨ Upgrade! ✨</a>