Polish content pages: share AuthTopBar, page-grid helper and responsive tables

- Extract shared AuthTopBar frosted top bar; reuse in login & register
- Add .page-grid class replacing 48 inline grid styles
- Add .table-scroll + .table-cell-truncate helpers; wrap leaderboard/staff tables
- Constrain settings page width (max-w-5xl) and stack profile card on mobile
- Use theme background var for shop category icon (dark-mode safe)

src/app/globals.css

@@ -1400,16 +1400,36 @@ a.content-card {
 	}
 }
 
+/* Rich content-page grid (replaces repeated inline `display:grid;gap:1.5rem`). */
+.page-grid {
+	display: grid;
+	gap: 1.5rem;
+}
+
 /* make tables scroll on small screens */
 @media (max-width: 640px) {
 	table {
+		display: table;
+	}
+	.table-scroll {
 		display: block;
 		overflow-x: auto;
 		-webkit-overflow-scrolling: touch;
 		border-radius: var(--radius-sm);
+		-ms-overflow-style: none;
+		scrollbar-width: thin;
 	}
 }
 
+/* Cell text truncation helper for dense tables so long values (motto, URLs)
+   collapse gracefully instead of blowing out row width on small screens. */
+.table-cell-truncate {
+	max-width: 14rem;
+	overflow: hidden;
+	text-overflow: ellipsis;
+	white-space: nowrap;
+}
+
 /* Safe-area insets for notched phones (header/nav/footer sit at screen edges) */
 @supports (padding: max(0px)) {
 	.site-header,