refactor: split admin.css monolith, standardize CSS architecture

- Split admin.css (3228 lines) into 12 focused files: variables, base,
  forms, buttons, layout, components, tables, skeleton, datepicker,
  filemanager, pagination, responsive
- Extracted shared styles from offers.css and dashboard.css into
  components.css and forms.css (offers-* → admin-* prefix)
- Standardized naming: dash-kpi-* → admin-kpi-*, session-* → dash-session-*,
  rich-editor → admin-rich-editor
- Deleted duplicate offers-tabs (using admin-tabs everywhere)
- Deduplicated DatePicker and FileManager CSS (~360 lines removed)
- Added 16 utility classes to base.css (font sizes, widths, gaps, margins)
- Deleted empty admin.css

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/admin/tables.css

@@ -0,0 +1,132 @@
+/* ============================================================================
+   Tables
+   ============================================================================ */
+
+.admin-table-wrapper,
+.admin-table-responsive {
+  overflow-x: auto;
+  -webkit-overflow-scrolling: touch;
+}
+
+.admin-table {
+  width: 100%;
+  min-width: 650px;
+  border-collapse: collapse;
+}
+
+.admin-table th {
+  text-align: left;
+  padding: 10px 16px;
+  font-size: 11px;
+  font-weight: 600;
+  color: var(--text-muted);
+  text-transform: uppercase;
+  letter-spacing: 0.05em;
+  border-bottom: 1px solid var(--border-color);
+  white-space: nowrap;
+}
+
+.admin-table td {
+  padding: 11px 16px;
+  border-bottom: 1px solid var(--border-color);
+  color: var(--text-secondary);
+  font-size: 13px;
+  line-height: 1.5;
+  white-space: nowrap;
+}
+
+.admin-table tr:last-child td {
+  border-bottom: none;
+}
+
+@media (max-width: 768px) {
+  .admin-table th,
+  .admin-table td {
+    padding: 8px 10px;
+    font-size: 12px;
+  }
+
+  .admin-table th {
+    font-size: 10px;
+  }
+
+  .admin-table-avatar {
+    width: 32px;
+    height: 32px;
+    font-size: 11px;
+  }
+
+  .admin-table-name {
+    font-size: 12px;
+  }
+
+  .admin-table-username {
+    font-size: 11px;
+  }
+}
+
+.admin-table-user {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  white-space: nowrap;
+}
+
+.admin-table-avatar {
+  width: 34px;
+  height: 34px;
+  border-radius: 50%;
+  background: var(--accent-light);
+  color: var(--accent-color);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  font-weight: 600;
+  font-size: 12px;
+}
+
+.admin-table-name {
+  font-weight: 500;
+  color: var(--text-primary);
+  white-space: nowrap;
+}
+
+.admin-table-username {
+  font-size: 13px;
+  color: var(--text-muted);
+  white-space: nowrap;
+}
+
+.admin-table-actions {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+}
+
+/* Tables - compact on mobile, better scroll indication */
+@media (max-width: 640px) {
+  .admin-table-wrapper,
+  .admin-table-responsive {
+    margin: 0 -1rem;
+    padding: 0 1rem;
+    position: relative;
+  }
+
+  .admin-table {
+    min-width: 500px;
+  }
+
+  .admin-table th,
+  .admin-table td {
+    padding: 8px;
+    font-size: 11px;
+  }
+
+  .admin-table th {
+    font-size: 9px;
+  }
+
+  .admin-table-actions {
+    gap: 0.25rem;
+  }
+}