fix: use 100dvh for body and #app to match dynamic viewport

Prevents white space below the app on Android Chrome where the
system nav bar makes 100vh > 100dvh.

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

src/styles/app.css

@@ -55,7 +55,7 @@ html {
 }
 
 body {
-  height: 100vh;
+  height: 100dvh;
   scroll-behavior: smooth;
   overflow-y: auto;
 }
@@ -78,7 +78,7 @@ body {
 }
 
 #app {
-  height: 100vh;
+  height: 100dvh;
   display: flex;
 }