feat(frontend): i18n expansion, admin/profile i18n, grid/list view fix, empty state

- Add 5 new locales (hi, ar, ru, ja, ko) — now 14 total
- Admin panel: 117 i18n keys, confirm modal, animated tabs, no inline handlers
- Profile page: 58 i18n keys with data-i18n attributes
- Fix i18n safeT() shadowing bug and translationsLoaded timing
- Fix grid/list view: list header no longer shows in grid mode on login
- Fix classList.toggle hidden sync for view switching across all nav functions
- Revert .hidden important that broke login page rendering
- Add files empty state (no_files + empty_hint) with translations
- Fix language selector dropdown scroll and styling
- Fix admin panel scroll with sticky tabs

static/css/base/variables.css

@@ -1,9 +1,35 @@
 :root {
+    /* Backgrounds */
     --color-bg-page: #f5f7fa;
     --color-bg-surface: #ffffff;
+    --color-bg-input: #f9fafb;
+    --color-bg-hover: #f8fafc;
+
+    /* Borders */
     --color-border: #e2e8f0;
+    --color-border-light: #f1f5f9;
+
+    /* Text */
     --color-text: #2d3748;
+    --color-text-heading: #1e293b;
     --color-text-muted: #718096;
+    --color-text-faint: #94a3b8;
+
+    /* Accent */
     --color-accent: #ff5e3a;
     --color-accent-hover: #e04520;
+    --color-accent-gradient: linear-gradient(135deg, #ff5e3a 0%, #ff2d55 100%);
+    --color-accent-shadow: rgba(255, 94, 58, 0.3);
+    --color-accent-ring: rgba(255, 94, 58, 0.1);
+    --color-accent-tint: #fff5f3;
+
+    /* Feedback */
+    --color-error-bg: #fee2e2;
+    --color-error-text: #b91c1c;
+    --color-success-bg: #dcfce7;
+    --color-success-text: #15803d;
+
+    /* Shadows */
+    --color-shadow: rgba(0, 0, 0, 0.1);
+    --color-shadow-lg: rgba(0, 0, 0, 0.12);
 }