fix: set page height to 100% instead of 100vh (#21025)

The PR modifies the page height from 100vh to 100% to prevent the content area from extending underneath the navbar on mobile devices:

- body, #outlet {
+ html, body, #outlet {
-   height: 100vh;
+   height: 100%;
    width: 100%;
    margin: 0;
  }

Author: vursen

flow-server/src/main/resources/com/vaadin/flow/server/frontend/index.html

@@ -8,8 +8,8 @@
   <meta charset="UTF-8" />
   <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover" />
   <style>
-    body, #outlet {
-      height: 100vh;
+    html, body, #outlet {
+      height: 100%;
       width: 100%;
       margin: 0;
     }