Strip spaces from generated decode report codes

generateSpecialCode() reused generateRandomString(), whose charset
includes a space. Across a 75-100 character code that made a space
almost certain, and /decode splits its argument on spaces, silently
truncating the code the player typed back in - breaking decoding.

Fixed at generation time rather than at display time, since the
stored value itself was the problem, not just how it's shown.
generateRandomString() is left untouched for its other use (the
"garbage" filler text shown to players who fail to decode), where
spaces are harmless.

src/Game/Service/GameResponseService.php

@@ -784,7 +784,9 @@ class GameResponseService
 
     private function generateSpecialCode(int $firstDigit, int $min, int $max): string
     {
-        $code = $this->generateRandomString($min, $max);
+        // No spaces: this code gets typed back in as a single /decode argument,
+        // which is split on spaces, so a space here would silently truncate it.
+        $code = str_replace(' ', '', $this->generateRandomString($min, $max));
 
         // Ensure the first numeric digit is the specified $firstDigit
         $found = false;