refactor(team): make server limit methods accept optional team parameter

Allow serverLimit() and serverLimitReached() to accept an optional team
parameter instead of relying solely on the current session. This improves
testability and makes the methods more flexible by allowing them to work
without session state.

Add comprehensive tests covering various scenarios including no session,
team at limit, and team under limit.

app/Http/Controllers/Api/HetznerController.php

@@ -586,7 +586,8 @@ class HetznerController extends Controller
         }
 
         // Check server limit
-        if (Team::serverLimitReached()) {
+        $team = Team::find($teamId);
+        if (Team::serverLimitReached($team)) {
             return response()->json(['message' => 'Server limit reached for your subscription.'], 400);
         }