[WIP] Fix fork-backed create_pull_request duplicate Authorization error

[Copilot]

• Move withGitHubHostToken to git_auth_helpers.cjs and export it (shared utility)
• Update push_to_pull_request_branch.cjs to import withGitHubHostToken from git_auth_helpers.cjs instead of defining it locally
• Update create_pull_request.cjs:
  • Import withGitHubHostToken from git_auth_helpers.cjs
  • Add cwd option to handleRemoteBranchCollision
  • Use withGitHubHostToken with cwd in handleRemoteBranchCollision instead of inline override/restore
  • Pass cwd to git ls-remote exec options in handleRemoteBranchCollision
  • Update all 3 call sites of handleRemoteBranchCollision to pass cwd: process.cwd()
• Add withGitHubHostToken tests in git_auth_helpers.test.cjs (5 new tests)
• Run make fmt and make agent-report-progress
• All 263 tests pass across modified files

• Fixes Fork-backed create_pull_request fails with duplicate Authorization HTTP 400 #48414

[github-actions]

PR Triage

• Category: bug | Risk: high | Score: 35/100
• Impact 20 · Urgency 10 · Quality 5
• Recommended action: defer

Explicitly marked [WIP] draft; diff is currently just a checklist (1 line changed), no substantive code yet. Defer until work is pushed and draft is removed.

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