cockpit: cellular WAN row with signal + Restart button

Include the gsm device in the WAN/Uplinks table, shown as its routed
netdev with IP and metric (nmcli actions still target cdc-wdm0). New
Signal column fed by mmcli -K in the single status spawn (percent, tech,
operator). Restart = mmcli disable/enable — the EC25 MBIM plugin doesn't
support --reset — with a USB unbind/bind fallback (vendor 2c7c) when
ModemManager can't reach the modem. README: modem setup steps (Koodo
profile creation, MBIM netdev gotcha, Cockpit row).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

cockpit/vanrouter/index.html

@@ -49,7 +49,7 @@
             <h3>WAN / Uplinks</h3>
             <table>
                 <thead>
-                    <tr><th>Device</th><th>Type</th><th>State</th><th>IPv4</th><th>Metric</th><th>Actions</th></tr>
+                    <tr><th>Device</th><th>Type</th><th>State</th><th>IPv4</th><th>Signal</th><th>Metric</th><th>Actions</th></tr>
                 </thead>
                 <tbody id="wan"></tbody>
             </table>