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">