refactor(admin): migrate section cards onto the shared card primitives

The admin tree hand-rolled its card surfaces and stepped padding at sm:
instead of md:, so it read denser than every other route on a tablet.
Move the sections onto SettingsCard/SettingsCardHeader and the mini-rows
onto ListRow; no behaviour, data, or copy changes.

src/components/admin/__tests__/api-token-overview-responsive.test.tsx

@@ -115,11 +115,12 @@ describe("ApiTokenOverviewSection — responsive", () => {
     expect(html).toContain("All");
   });
 
-  it("uses a smaller card padding on mobile (p-4 sm:p-6)", () => {
+  it("uses a smaller card padding on mobile (p-4 md:p-6)", () => {
     const html = render();
-    // The card root carries the responsive padding to leave more room
-    // for content within a 393 CSS-px viewport.
-    expect(html).toMatch(/class="[^"]*\bp-4\b[^"]*sm:p-6/);
+    // The card root carries the shared SettingsCard padding contract
+    // (`p-4 md:p-6`) to leave more room for content within a 393 CSS-px
+    // viewport while stepping up only from `md`, not `sm`.
+    expect(html).toMatch(/class="[^"]*\bp-4\b[^"]*md:p-6/);
   });
 
   it("desktop date cells drop whitespace-nowrap (v1.4.22 C2 5th-attempt fix)", () => {

src/components/admin/__tests__/user-management-responsive.test.tsx

@@ -115,9 +115,9 @@ describe("UserManagementSection — mobile responsive", () => {
     expect(mobileSlice).toContain("Force logout");
   });
 
-  it("uses smaller card padding on mobile (p-4 sm:p-6)", () => {
+  it("uses smaller card padding on mobile (p-4 md:p-6)", () => {
     const html = render();
-    expect(html).toMatch(/class="[^"]*\bp-4\b[^"]*sm:p-6/);
+    expect(html).toMatch(/class="[^"]*\bp-4\b[^"]*md:p-6/);
   });
 
   it("wraps the filter pills below the title on narrow viewports", () => {