fix: force sync before boss fight and surface challenge errors to UI (#64)

Closes #50

## Summary
- Calls `forceSync()` before every boss challenge so the server always fights against the player's live state (equipped items, upgrades, etc.) rather than a potentially stale snapshot
- Adds a `bossError` state that captures and displays error messages from failed manual boss challenges in the boss panel, matching the existing `autoBossError` display pattern

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #64
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

apps/web/src/components/game/bossPanel.tsx

@@ -235,6 +235,7 @@ const BossPanel = (): JSX.Element => {
     toggleAutoBoss,
     autoBossLastResult,
     autoBossError,
+    bossError,
   } = useGame();
   const [ challengingBossId, setChallengingBossId ] = useState<string | null>(
     null,
@@ -362,6 +363,13 @@ const BossPanel = (): JSX.Element => {
         </div>
       </div>
 
+      {bossError === null
+        ? null
+        : <p className="auto-boss-error">
+          {"⚠️ "}
+          {bossError}
+        </p>
+      }
       {autoBossError === null
         ? null
         : <p className="auto-boss-error">

apps/web/src/context/gameContext.tsx

@@ -557,6 +557,12 @@ interface GameContextValue {
    * when no error). Cleared automatically when the player re-enables auto-boss.
    */
   autoBossError: string | null;
+
+  /**
+   * Error message from the most recent manual boss challenge (null when no
+   * error). Cleared automatically when a new challenge is initiated.
+   */
+  bossError: string | null;
 }
 
 export interface BattleResult {
@@ -606,6 +612,7 @@ export const GameProvider = ({
     at:       number;
   } | null>(null);
   const [ autoBossError, setAutoBossError ] = useState<string | null>(null);
+  const [ bossError, setBossError ] = useState<string | null>(null);
   const syncErrorTimerReference = useRef<ReturnType<typeof setTimeout> | null>(
     null,
   );
@@ -1867,6 +1874,14 @@ export const GameProvider = ({
       return;
     }
 
+    setBossError(null);
+
+    /*
+     * Flush any pending state (e.g. newly equipped items) to the server before
+     * the fight so the server-side calculation uses the player's live stats.
+     */
+    await forceSync();
+
     try {
       const result = await challengeBossApi({ bossId });
       setState((previous) => {
@@ -1878,9 +1893,13 @@ export const GameProvider = ({
       setBattleResult({ bossName: boss.name, result: result });
     } catch (error_: unknown) {
       logError("challenge_boss", error_);
-      // Silently ignore — server errors shouldn't crash the UI
+      setBossError(
+        error_ instanceof Error
+          ? error_.message
+          : "Failed to challenge boss",
+      );
     }
-  }, []);
+  }, [ forceSync ]);
 
   const dismissOfflineGold = useCallback(() => {
     setOfflineGold(0);
@@ -2023,6 +2042,7 @@ export const GameProvider = ({
       autoBossError,
       autoBossLastResult,
       battleResult,
+      bossError,
       buyAdventurer,
       buyEchoUpgrade,
       buyEquipment,
@@ -2091,6 +2111,7 @@ export const GameProvider = ({
     autoBossError,
     autoBossLastResult,
     battleResult,
+    bossError,
     completedQuestToasts,
     failedQuestToasts,
     formatNumber,