Scope remote servers to specific projects

What problem will this feature address?

Remote servers are currently global — once added, they appear in the server selector for every project. When managing client deployments on their servers alongside your own projects, this creates clutter and confusion:

• Client servers show up when deploying internal projects
• Your own servers show up when working on client projects
• Risk of accidentally deploying to the wrong server

Describe the solution you would like

Allow associating a remote server with a specific project (or set of projects):

1. When adding a remote server, optionally scope it to one or more projects
2. Scoped servers only appear in the server selector within those projects
3. Global servers (no scope) behave as they do today — available everywhere
4. A server can be both scoped to specific projects and available globally (toggle)

Example workflow

Project: "Client A — Website"
  → Remote server: client-a-vps (scoped to this project only)
  → Services deploy to client-a-vps

Project: "Polyhelper"  
  → Uses default server (global)
  → Does NOT see client-a-vps in the dropdown

Additional context

This would pair well with project folders/tags (#3703) to create a clean separation between different deployment contexts (internal vs client work).

Start by tracing how remote servers are created and how the project server selector loads its options; the issue does not name specific files or tests. Review the existing project and server data relationships, then define and verify scoped, global, and combined visibility behavior for deployments.