Add ValidProxyConfigFilename rule for dynamic proxy config validation

Adds a new Laravel validation rule to prevent path traversal, hidden files, and invalid filenames in the dynamic proxy configuration feature. Validates filenames to ensure they contain only safe characters, don't exceed filesystem limits, and don't use reserved names.

- New Rule: ValidProxyConfigFilename with comprehensive validation
- Updated: NewDynamicConfiguration to use the new rule
- Added: 13 unit tests covering all validation scenarios

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/Livewire/Server/Proxy/NewDynamicConfiguration.php

@@ -4,6 +4,7 @@ namespace App\Livewire\Server\Proxy;
 
 use App\Enums\ProxyTypes;
 use App\Models\Server;
+use App\Rules\ValidProxyConfigFilename;
 use Illuminate\Foundation\Auth\Access\AuthorizesRequests;
 use Livewire\Component;
 use Symfony\Component\Yaml\Yaml;
@@ -38,11 +39,11 @@ class NewDynamicConfiguration extends Component
         try {
             $this->authorize('update', $this->server);
             $this->validate([
-                'fileName' => 'required',
+                'fileName' => ['required', new ValidProxyConfigFilename],
                 'value' => 'required',
             ]);
 
-            // Validate filename to prevent command injection
+            // Additional security validation to prevent command injection
             validateShellSafePath($this->fileName, 'proxy configuration filename');
 
             if (data_get($this->parameters, 'server_uuid')) {