Split Event Manager's race-mode page into tabs

The race-mode management page (participants, teams, race format,
live grid/standings, and now the schedule/print tools) had grown into
a long scroll. Grouped into four tabs - Participants & teams, Format,
Live & results, Schedule & print - matching the tab pattern already
used for Settings. Only wrapper divs were added; no section's markup
or event bindings moved. The existing step-card overview and warning
links now switch to the right tab before jumping to it, and Open Grid
switches to the Live tab so its target is actually visible. Track/
sponsor events, which never had this length problem, are unaffected.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/styles.css

@@ -1588,6 +1588,42 @@ body {
   display: none;
 }
 
+.manage-tabs {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+  margin: 14px 0;
+}
+
+.manage-tab {
+  border: 1px solid var(--line);
+  background: var(--surface-soft);
+  color: var(--text);
+  border-radius: 10px;
+  padding: 8px 14px;
+  cursor: pointer;
+  font-weight: 600;
+  font-size: 0.86rem;
+  transition: all 0.2s ease;
+}
+
+.manage-tab:hover {
+  border-color: color-mix(in srgb, var(--accent-2) 42%, var(--line));
+}
+
+.manage-tab.active {
+  border-color: color-mix(in srgb, var(--accent) 55%, transparent);
+  background: linear-gradient(
+    90deg,
+    color-mix(in srgb, var(--accent) 30%, transparent),
+    color-mix(in srgb, var(--accent) 10%, transparent)
+  );
+}
+
+[data-manage-panel][hidden] {
+  display: none;
+}
+
 .decoder-settings-form {
   display: grid;
   gap: 16px;