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/Models/Server.php

@@ -523,6 +523,11 @@ $schema://$host {
         return $this->proxy->modelScope();
     }
 
+    public function scopeWhereProxyType(Builder $query, string $proxyType): Builder
+    {
+        return $query->where('proxy->type', $proxyType);
+    }
+
     public function isLocalhost()
     {
         return $this->ip === 'host.docker.internal' || $this->id === 0;