Fix IPA/syllable first-click not working (off-by-one in initialLoadDone)

The old guard checked if grid was loaded AND set initialLoadDone in
the same pass, then returned without rebuilding. This meant the first
user-triggered mode change was always swallowed.

Simplified to a mount-skip ref: skip exactly the first useEffect trigger
(component mount), rebuild on every subsequent trigger (user changes).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

admin-lehrer/components/grid-editor/useGridEditor.ts

@@ -105,10 +105,11 @@ export function useGridEditor(sessionId: string | null) {
   // We call the API directly with the new values instead of going through
   // the buildGrid callback, which may still close over stale state due to
   // React's asynchronous state batching.
-  const initialLoadDone = useRef(false)
+  const mountedRef = useRef(false)
   useEffect(() => {
-    if (!initialLoadDone.current) {
-      if (grid) initialLoadDone.current = true
+    if (!mountedRef.current) {
+      // Skip the first trigger (component mount) — don't rebuild yet
+      mountedRef.current = true
       return
     }
     if (!sessionId) return