chore: more feedback fixes (#129)

## Summary

- Fix `NaN` displayed in Sync New Content / Force Unlock notifications by guarding against undefined counts
- Poll server for exploration claimability before showing Collect button to prevent client/server desync
- Return authoritative materials list from craft API to prevent client desync causing false affordability
- Add test coverage for `sync-new-content` and `explore/claimable` endpoints

Closes #125
Closes #127
Closes #128

## Test plan

- [ ] Trigger a sync with new content and verify the notification shows a real count instead of `NaN`
- [ ] Start an exploration, wait for it to complete, and verify the Collect button only appears after the server confirms claimable
- [ ] Attempt to craft a recipe and verify the material counts in the UI update to match the server's authoritative values

✨ This issue was created with help from Hikari~ 🌸

Reviewed-on: #129
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

apps/web/src/api/client.ts

@@ -17,6 +17,7 @@ import type {
   BuyPrestigeUpgradeResponse,
   CraftRecipeRequest,
   CraftRecipeResponse,
+  ExploreClaimableResponse,
   ExploreCollectRequest,
   ExploreCollectResponse,
   ExploreStartRequest,
@@ -244,6 +245,19 @@ const collectExploration = async(
   });
 };
 
+/**
+ * Checks whether a given exploration area is ready to claim on the server.
+ * @param areaId - The area ID to check.
+ * @returns Whether the exploration is claimable.
+ */
+const checkExplorationClaimable = async(
+  areaId: string,
+): Promise<ExploreClaimableResponse> => {
+  return await fetchJson<ExploreClaimableResponse>(
+    `/explore/claimable?areaId=${encodeURIComponent(areaId)}`,
+  );
+};
+
 /**
  * Crafts a recipe on the server.
  * @param body - The craft recipe request payload.
@@ -316,6 +330,7 @@ export {
   buyEchoUpgrade,
   buyPrestigeUpgrade,
   challengeBoss,
+  checkExplorationClaimable,
   collectExploration,
   craftRecipe,
   debugHardReset,