fix(deployment): resolve shared env vars using main server

Use `$this->mainServer` when resolving environment variable values across
deployment env generation (runtime, buildtime, nixpacks, args, and secrets
hash) so shared server-scoped values are applied consistently.

Also add `server_id` to `SharedEnvironmentVariable::$fillable` and normalize
the Livewire Blade file newline.

app/Models/SharedEnvironmentVariable.php

@@ -17,6 +17,7 @@ class SharedEnvironmentVariable extends Model
         'team_id',
         'project_id',
         'environment_id',
+        'server_id',
 
         // Boolean flags
         'is_multiline',