feat(site-status-checker): add Live Site Preview webview for Site tab

A Scarf project dashboard that includes at least one webview widget
automatically exposes a Site tab next to the Dashboard tab. Adding a
"Live Site Preview" section with a webview widget gives this template
that tab out of the box.

The cron job + AGENTS.md now tell the agent to rewrite the webview's
`url` field to the first entry in `values.sites` on each run, so the
Site tab renders whatever the user actually configured instead of the
GitHub placeholder. If `values.sites` is empty, the webview URL is
left untouched.

Swift example test updated to assert 4 sections (was 3) plus the new
webview widget's presence + title; bundle + catalog rebuilt.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

templates/catalog.json

@@ -7,8 +7,8 @@
         "name": "Alan Wizemann",
         "url": "https://github.com/awizemann/scarf"
       },
-      "bundleSha256": "a3c3a3b1cd1799443fa32ac5f1f643bf28b2e1b30c1b7786a1fa93ef227b0c7e",
-      "bundleSize": 7197,
+      "bundleSha256": "2a4e0aba5bd4d86be3153d87c6ce219b9068223daebfad6f9db2b82c3752fac5",
+      "bundleSize": 7583,
       "category": "monitoring",
       "config": {
         "modelRecommendation": {