Consolidate tab persistence logic into Tabs component

- Move active tab persistence into Tabs component with storageKey + activeTabKey props
- Change value prop to defaultValue so callers don't manage tab state
- Add TabsRef with setActiveTab method for programmatic tab switching
- Restore request_pane.focus_tab listener for :param placeholder clicks
- Update all Tab consumers to use new pattern

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src-web/hooks/useRequestEditor.tsx

@@ -34,7 +34,7 @@ export function useRequestEditor() {
   const focusParamValue = useCallback(
     (name: string) => {
       focusParamsTab();
-      setTimeout(() => emitter.emit('request_params.focus_value', name), 50);
+      requestAnimationFrame(() => emitter.emit('request_params.focus_value', name));
     },
     [focusParamsTab],
   );