Fix wallet top-up button to link directly to top-up page

- Replace placeholder alert with functional wallet top-up link
- Update wallet_card.html to use {% url 'wallet:wallet_topup' %}
- Change from button to anchor tag with proper styling
- Links directly to /wallet/topup/ for immediate top-up access
- Affects all agent pages using the shared wallet card component

🤖 Generated with [Claude Code](https://claude.ai/code)

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

templates/components/wallet_card.html

@@ -10,8 +10,8 @@
         <div class="balance-label">Available Balance</div>
     </div>
     <div style="margin-top: 12px;">
-        <button type="button" class="wallet-topup-btn" style="width: 100%; padding: 8px 16px; background: linear-gradient(135deg, #4f46e5, #7c3aed); color: white; border: none; border-radius: 8px; font-size: 13px; font-weight: 500; cursor: pointer; transition: all 0.2s;" onclick="alert('Top-up feature coming soon!')">
+        <a href="{% url 'wallet:wallet_topup' %}" class="wallet-topup-btn" style="display: block; width: 100%; padding: 8px 16px; background: linear-gradient(135deg, #4f46e5, #7c3aed); color: white; border: none; border-radius: 8px; font-size: 13px; font-weight: 500; cursor: pointer; transition: all 0.2s; text-decoration: none; text-align: center; box-sizing: border-box;">
             💳 Top Up Wallet
-        </button>
+        </a>
     </div>
 </div>