fix(performance): eliminate N+1 query in CheckTraefikVersionJob

This commit fixes a critical N+1 query issue in CheckTraefikVersionJob
that was loading ALL proxy servers into memory then filtering in PHP,
causing potential OOM errors with thousands of servers.

Changes:
- Added scopeWhereProxyType() query scope to Server model for
  database-level filtering using JSON column arrow notation
- Updated CheckTraefikVersionJob to use new scope instead of
  collection filter, moving proxy type filtering into the SQL query
- Added comprehensive unit tests for the new query scope

Performance impact:
- Before: SELECT * FROM servers WHERE proxy IS NOT NULL (all servers)
- After: SELECT * FROM servers WHERE proxy->>'type' = 'TRAEFIK' (filtered)
- Eliminates memory overhead of loading non-Traefik servers
- Critical for cloud instances with thousands of connected servers

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

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

app/Jobs/CheckTraefikVersionJob.php

@@ -47,10 +47,10 @@ class CheckTraefikVersionJob implements ShouldQueue
 
             // Query all servers with Traefik proxy that are reachable
             $servers = Server::whereNotNull('proxy')
+                ->whereProxyType(ProxyTypes::TRAEFIK->value)
                 ->whereRelation('settings', 'is_reachable', true)
                 ->whereRelation('settings', 'is_usable', true)
-                ->get()
-                ->filter(fn ($server) => $server->proxyType() === ProxyTypes::TRAEFIK->value);
+                ->get();
 
             $serverCount = $servers->count();
             Log::info("CheckTraefikVersionJob: Found {$serverCount} server(s) with Traefik proxy");