feat: Docker network management with per-resource attachment

[BSalaeddin]

Adds first-class Docker network management to Dokploy — create, delete, and attach networks to any application or database service.

What changed

• New Networks page in the sidebar for managing Docker networks across servers
• Per-resource network attachment cards on each application and database service page
• Support for bridge and overlay drivers, with server scoping
• Duplicate name detection with user-friendly error messages
• Blocked deletion of networks that are still attached to services
• Migrations add network table and resource relation columns

Migration

New network table and junction columns on application + 6 database schemas. Non-breaking — existing services continue working without networks attached.