fix(ui): remove redundant app-shell top gap (sticky nav double-offset)

Every view showed a large empty band at the top (operator-flagged during the
Vuetify-4 review; pre-existing). Cause: .fc-content had padding-top:64px to clear
the navbar, but TopNav is position:sticky and already reserves its own space in
the v-app flex column — the 64px was a fixed-navbar leftover that double-counted
the offset. Removed it; content now flows directly below the sticky nav (and the
full-height calc(100vh-64px) views no longer overflow).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/AppShell.vue

@@ -18,11 +18,11 @@ const route = useRoute()
 <style scoped>
 .fc-content {
   min-height: 100vh;
-  /* Push initial viewport content below the sticky TopNav. Without
+  /* NO padding-top: the TopNav is position:sticky, so it already reserves its
-     this, some views' first rows / form fields / table headers can
+     own space in the v-app flex column — content flows directly below it. The
-     end up obscured by the navbar (depending on parent overflow
+     old 64px padding-top was a leftover from a FIXED navbar and double-counted
-     context interacting with position: sticky). Scrolled-down content
+     that space, leaving a large empty band at the top of EVERY view (and pushing
-     still slides under the nav — the gradient-fade design is intact. */
+     the full-height calc(100vh - 64px) views down so they overflowed). Removed
-  padding-top: 64px;
+     2026-07-13. Scrolled content still slides under the sticky nav as before. */
 }
 </style>