Fix RADIUS key default — replace double-encoded value with correct plaintext

The previous default (NZXMkUA62QZHfG3FTYNCz4Y) was already base64-encoded,
causing the config generator to double-encode it via b64(). Updated to the
correct plaintext key (4VXMKUA62QZHFG3FTYNCZ4Y) so b64() produces the right
key-encrypted value in the switch config output.

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

templates/index.html

@@ -736,7 +736,7 @@
             </div>
             <div class="setting-item full">
               <span class="setting-label">RADIUS KEY (plaintext)</span>
-              <input type="text" id="s-radius" value="NZXMkUA62QZHfG3FTYNCz4Y">
+              <input type="text" id="s-radius" value="4VXMKUA62QZHFG3FTYNCZ4Y">
             </div>
             <div class="setting-item full">
               <span class="setting-label">SNMP AUTH (checkmk)</span>