feat: nav 4x2 button grid + hero stats from correct chains

- Replace nav menu with 4x2 mobile-app-style button grid (responsive)
- Fetch staking stats from Asset Hub instead of Relay Chain
- Governance stats (proposals, voters) remain on Relay Chain
- Trust score: show login prompt for guests, real score for users
- Full-width root container, centered hero, node globals shim fix

web/src/App.css

@@ -1,8 +1,6 @@
 #root {
-  max-width: 1280px;
-  margin: 0 auto;
-  padding: 2rem;
-  text-align: center;
+  width: 100%;
+  min-height: 100vh;
 }
 
 .logo {
@@ -50,4 +48,4 @@
 
 .read-the-docs {
   color: #5f7676;
-}
+}