fix: ensure shell-content fills available viewport height

The terminal page uses height: 100% but parent .shell-content didn't
have explicit height, so the terminal couldn't fill the viewport.

Changes:
- .shell-content: added height: 100%
- .shell-body: added flex: 1 to fill flex parent
- Mobile .shell-content: added height: 100%

This ensures the terminal wrapper can properly calculate and fill
the available viewport space.

apps/web/src/styles.css

@@ -121,6 +121,7 @@ a {
   display: grid;
   grid-template-columns: 230px 1fr;
   min-height: calc(100vh - 57px);
+  flex: 1;
 }
 
 .shell-nav {
@@ -169,6 +170,7 @@ a {
   display: flex;
   flex-direction: column;
   min-height: 0;
+  height: 100%;
 }
 
 .eyebrow {
@@ -305,6 +307,7 @@ a {
 
   .shell-content {
     padding: var(--space-4);
+    height: 100%;
   }
 }