refactor(fe): centralize footer exclusion to base.css - single source of truth

Changes:
  • base.css: Add global footer hiding rule (applies to all .ks-page__footer, .ks-shell__footer, footer[class*=ks-])
  • PageLayout: Remove individual footer CSS (use global rule)
  • AppShellLayout: Remove individual footer CSS (use global rule)

Benefits:
  ✓ Single source of truth (base.css)
  ✓ Easier to maintain and update globally
  ✓ Consistent behavior across all layouts
  ✓ Can enable/disable with one change if needed
  ✓ Structure preserved (v-if, grid-areas intact)

Design principle: Single-screen + content-first
  • All controls in header/command-bar/summary
  • Recover ~48-64px per page for content
  • Mobile-friendly (no hard-to-reach footer)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

frontend/src/design-system/base.css

@@ -122,3 +122,12 @@ button, .p-button, .ks-button {
 .p-dialog-footer, .ks-dialog__footer {
   padding: var(--ks-space-3) var(--ks-space-4) !important;
 }
+
+/* Global Footer Exclusion: Single-Screen Principle */
+/* All footers hidden (both page-level and global) to maximize content area */
+/* Structure preserved for backward compatibility; CSS hiding only */
+.ks-page__footer,
+.ks-shell__footer,
+footer[class*="ks-"] {
+  display: none !important; /* Maximize viewport for content; all controls → header/command-bar/summary */
+}