Add project-github-token support for campaign specs

[Copilot]

Campaign specs need to configure GitHub tokens for Projects v2 operations, but the token configuration wasn't being serialized into generated .g.campaign.md files, requiring manual edits after generation.

Changes

• Campaign spec: Added project-github-token field to CampaignSpec struct
• Orchestrator builder: Pass token from spec to UpdateProjectConfig.GitHubToken when specified
• Markdown generation: Serialize github-token field in safe-outputs YAML when token is configured
• Tests: Added coverage for token flow through builder and markdown generation

Example

Campaign spec (.campaign.md):

project-url: "https://github.com/orgs/githubnext/projects/60"
project-github-token: "${{ secrets.GH_AW_PROJECT_GITHUB_TOKEN }}"

Generated orchestrator (.campaign.g.md):

safe-outputs:
    update-project:
        github-token: ${{ secrets.GH_AW_PROJECT_GITHUB_TOKEN }}
        max: 10

Token is omitted from output when not specified in spec, maintaining backward compatibility.

Original prompt

For campaigns, we are still missing the coding pattern:

safe-outputs:
  update-project:
    github-token: ${{ secrets.GH_AW_PROJECT_GITHUB_TOKEN }}

But campaigns are just specs... this somehow needs to be added to the generated .g.campaign.md file...

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