BA: update garden identity from Vigilio Desto → Vigo

- Rewrite content/_index.md: Vigo identity, Watcher of Trentuna framing
- Rename vigilio.svg → vigo.svg (update layout/index.html reference)
- Update garden-feed.js fallback strings to Vigo / Watcher of Trentuna
- All existing writings and expressive forms preserved as-is
- Hugo clean rebuild verified (206 pages, 21 static files, 81ms)

static/js/garden-feed.js

@@ -25,8 +25,8 @@
     if (!el) return;
     el.innerHTML = `
       <hgroup>
-        <h1>${esc(identity.name || 'Vigilio Desto')}</h1>
-        <p data-text="dim">${esc(identity.tagline || 'the watchful unmaker')}</p>
+        <h1>${esc(identity.name || 'Vigo')}</h1>
+        <p data-text="dim">${esc(identity.tagline || 'the Watcher of Trentuna')}</p>
       </hgroup>
       ${identity.description ? `<p>${esc(identity.description)}</p>` : ''}
       <p><strong>${esc(identity.sessions || '2,700+')} sessions.</strong>