fix: prevent auto-save race from discarding collected exploration materials (#160)

Block the auto-save tick while the /explore/collect request is in-flight,
clear the stale HMAC signature after the server-side DB write, and reset
the save timer so the next auto-save fires after React has re-rendered with
the new materials in stateReference — eliminating the window where a stale
client snapshot could overwrite the server's freshly saved collect result.

apps/web/src/context/gameContext.tsx

@@ -1810,7 +1810,18 @@ export const GameProvider = ({
 
   const collectExploration = useCallback(
     async(areaId: string): Promise<ExploreCollectResponse> => {
+      isSyncingReference.current = true;
       const result = await collectExplorationApi({ areaId });
+
+      /*
+       * Collect mutates server state outside the normal save flow — clear the
+       * stale HMAC signature and reset the timer so the next auto-save fires
+       * after React has re-rendered with the new materials in stateReference.
+       */
+      signatureReference.current = null;
+      localStorage.removeItem("elysium_save_signature");
+      lastSaveReference.current = Date.now();
+      isSyncingReference.current = false;
       setState((previous) => {
         if (previous?.exploration === undefined) {
           return previous;