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/pagination.css

@@ -0,0 +1,91 @@
+/* ============================================================================
+   Pagination
+   ============================================================================ */
+
+.admin-pagination {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: 0.75rem;
+  padding: 0.75rem 1rem;
+  margin-top: 0.5rem;
+  border-top: 1px solid var(--border-color);
+  font-size: 13px;
+}
+
+.admin-pagination-info {
+  color: var(--text-muted);
+  font-family: var(--font-mono);
+  font-size: 12px;
+  white-space: nowrap;
+}
+
+.admin-pagination-controls {
+  display: flex;
+  align-items: center;
+  gap: 2px;
+}
+
+.admin-pagination-page {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 32px;
+  height: 32px;
+  padding: 0 6px;
+  border: 1px solid transparent;
+  border-radius: var(--border-radius-sm);
+  background: none;
+  color: var(--text-secondary);
+  font-size: 13px;
+  font-family: var(--font-mono);
+  cursor: pointer;
+  transition:
+    background 0.15s,
+    color 0.15s,
+    border-color 0.15s;
+}
+
+.admin-pagination-page:hover {
+  background: var(--bg-secondary);
+  color: var(--text-primary);
+}
+
+.admin-pagination-page.active {
+  background: var(--accent-color);
+  color: #fff;
+  border-color: var(--accent-color);
+  font-weight: 600;
+}
+
+.admin-pagination-ellipsis {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 28px;
+  color: var(--text-muted);
+  font-size: 14px;
+}
+
+.admin-pagination-select {
+  padding: 4px 8px;
+  border: 1px solid var(--border-color);
+  border-radius: var(--border-radius-sm);
+  background: var(--bg-primary);
+  color: var(--text-secondary);
+  font-size: 12px;
+  cursor: pointer;
+}
+
+@media (max-width: 640px) {
+  .admin-pagination {
+    flex-wrap: wrap;
+    gap: 0.5rem;
+  }
+
+  .admin-pagination-info {
+    order: 2;
+    width: 100%;
+    text-align: center;
+  }
+}