Add `minimal_output` parameter to list_pull_requests and search_pull_requests

[mattbarr-g]

Describe the feature or problem you'd like to solve

The list_pull_requests and search_pull_requests tools return extremely verbose responses that, even for small result
sets.

Example: Listing 30 PRs returned 508KB of data (~17KB per PR), most of which is redundant metadata:

• Each PR includes full user objects with 15+ URL template fields
• assignee and assignees[] repeat the same user object structure
• reactions object with 10 fields (mostly zeros)
• Multiple *_url fields that follow predictable patterns

For a simple "show me my review queue" query returning 14 PRs, the response was ~36KB per PR.

Proposed solution

Add minimal_output parameter (like search_repositories already has) to:

• list_pull_requests
• search_pull_requests

When minimal_output: true, return only essential fields:

{
  "number": 6617,
  "title": "allow for no PDP filter in analytics",
  "state": "open",
  "draft": false,
  "user_login": "ThomasRochais",
  "created_at": "2026-02-02T13:05:54Z",
  "updated_at": "2026-02-02T13:53:18Z",
  "html_url": "https://github.com/org/repo/pull/6617",
  "head_ref": "feature-branch",
  "base_ref": "main"
}

This would reduce response size significantly.

Example prompts or workflows

1. "Show me PRs I need to review"
2. "List open PRs in this repo"
3. "Find PRs by author X"

Additional context

- search_repositories already implements minimal_output - this extends that pattern