Feature Request: Support multiple GitHub hosts in a single view

Is your feature request related to a problem?

I work with repositories across both github.com and our GitHub Enterprise instance. Currently, gh-dash only supports connecting to one GitHub host at a time via the GH_HOST environment variable. This means I cannot view PRs and issues from both github.com and our GHE instance simultaneously in one dashboard.

The current workaround is to either:

• Constantly switch the GH_HOST environment variable and restart gh-dash
• Use shell aliases (e.g., gh vs ghe) to run separate instances of gh-dash
• Only monitor one GitHub instance at a time

This creates friction for teams that maintain both public open-source projects and private enterprise code.

Describe the solution you'd like

Add support for configuring GitHub hosts at the section or repository level, allowing a single gh-dash instance to aggregate data from multiple GitHub instances.

Proposed configuration syntax:

Option 1: Host per section

prSections:
  - title: Public OSS PRs
    filters: is:open author:@me
    host: github.com

  - title: Enterprise PRs
    filters: is:open author:@me
    host: github.enterprise.example.com

  - title: Enterprise Team PRs
    filters: is:open org:my-team
    host: github.enterprise.example.com

Option 2: Full URL support in filters

prSections:
  - title: Mixed View
    filters: |
      is:open author:@me repo:myorg/public-repo OR
      is:open author:@me repo:github.enterprise.example.com/enterprise-org/private-repo

Expected behavior

• Each section could query its configured host independently
• The UI would optionally display which host each PR/issue belongs to (perhaps in the repo column or as an icon)
• All existing features (checkout, view, comment, etc.) would work regardless of which host the item belongs to

Alternative considerations

• The gh CLI already supports multiple authenticated hosts via gh auth login --hostname, so authentication infrastructure exists
• Each section could inherit a default host if not specified (current GH_HOST or github.com)
• This would be backward compatible - existing configs without host specification would continue to work

Additional context

Being able to monitor both in a unified dashboard would significantly improve the developer experience.