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/api/src/routes/explore.ts

@@ -7,6 +7,7 @@
 /* eslint-disable max-lines-per-function -- Route handlers require many steps */
 /* eslint-disable max-statements -- Route handlers require many statements */
 /* eslint-disable complexity -- Route handlers have inherent complexity */
+/* eslint-disable max-lines -- Route file requires multiple handlers */
 import { Hono } from "hono";
 import { defaultExplorations } from "../data/explorations.js";
 import { initialExploration } from "../data/initialState.js";
@@ -15,6 +16,7 @@ import { authMiddleware } from "../middleware/auth.js";
 import { logger } from "../services/logger.js";
 import type { HonoEnvironment } from "../types/hono.js";
 import type {
+  ExploreClaimableResponse,
   ExploreCollectEventResult,
   ExploreCollectRequest,
   ExploreCollectResponse,
@@ -49,6 +51,64 @@ const pickNothingMessage = (): string => {
   return nothingMessages[index] ?? nothingMessages[0] ?? "";
 };
 
+exploreRouter.get("/claimable", async(context) => {
+  try {
+    const discordId = context.get("discordId");
+    const areaId = context.req.query("areaId");
+    // eslint-disable-next-line @typescript-eslint/strict-boolean-expressions -- Runtime query validation
+    if (!areaId) {
+      return context.json({ error: "areaId is required" }, 400);
+    }
+
+    const explorationArea = defaultExplorations.find((a) => {
+      return a.id === areaId;
+    });
+    if (!explorationArea) {
+      return context.json({ error: "Unknown exploration area" }, 404);
+    }
+
+    const record = await prisma.gameState.findUnique({ where: { discordId } });
+    if (!record) {
+      return context.json({ error: "No save found" }, 404);
+    }
+
+    const rawState: unknown = record.state;
+    /* eslint-disable-next-line @typescript-eslint/consistent-type-assertions -- Prisma returns JsonValue; cast to GameState */
+    const state = rawState as GameState;
+
+    if (!state.exploration) {
+      const response: ExploreClaimableResponse = { claimable: false };
+      return context.json(response);
+    }
+
+    const area = state.exploration.areas.find((a) => {
+      return a.id === areaId;
+    });
+
+    if (!area || area.status !== "in_progress") {
+      const response: ExploreClaimableResponse = { claimable: false };
+      return context.json(response);
+    }
+
+    // eslint-disable-next-line capitalized-comments -- v8 ignore
+    /* v8 ignore next -- @preserve */
+    const startedAt = area.startedAt ?? 0;
+    const durationMs = explorationArea.durationSeconds * 1000;
+    const expiresAt = startedAt + durationMs;
+    const claimable = Date.now() >= expiresAt;
+    const response: ExploreClaimableResponse = { claimable };
+    return context.json(response);
+  } catch (error) {
+    void logger.error(
+      "explore_claimable",
+      error instanceof Error
+        ? error
+        : new Error(String(error)),
+    );
+    return context.json({ error: "Internal server error" }, 500);
+  }
+});
+
 exploreRouter.post("/start", async(context) => {
   try {
     const discordId = context.get("discordId");