Support VS Code-like proxy settings for MCP connections in Copilot Desktop (http.proxy, Kerberos principal, strict SSL)

### Feature summary

Copilot Desktop currently does not provide a way to configure MCP outbound traffic with proxy settings equivalent to VS Code network settings (such as http.proxy, Kerberos service principal, and strict SSL behavior).

### What problem are you trying to solve?

Problem
In enterprise environments, MCP endpoints are reachable only through a corporate proxy.
With VS Code, this is manageable through built-in proxy settings.
In Copilot Desktop, there is no clear/app-level configuration for the same behavior, which prevents reliable MCP connectivity in these setups.

Expected behavior
Copilot Desktop should support proxy configuration for MCP traffic with options functionally.

MCP server can be configured via URL, but app-level proxy controls are not exposed.
VS Code proxy settings cannot be reused directly in Copilot Desktop.
Enterprise auth/proxy scenarios (especially Kerberos) are difficult or impossible to configure predictably.
Why this matters
This blocks or complicates MCP adoption in corporate networks where direct outbound access is restricted and proxy + enterprise auth is mandatory.

### Proposed solution

Add explicit proxy settings support in Copilot Desktop for MCP connectivity, including:

Proxy URL configuration
Kerberos service principal support
Strict SSL toggle (or certificate trust controls)
Clear documentation on precedence between app settings, OS proxy, and environment variables
Request
Please confirm whether this is planned and, if possible, provide a timeline or workaround guidance for enterprise proxy + Kerberos MCP scenarios.

### Workflow impact

_No response_

### Installation context

_No response_

### Additional context

_No response_