refactor: standardize short project field handling

[mnkiefer]

• Standardizes and simplifies how the project field is handled in workflow frontmatter:
  • project field must now always be a URL string
    e.g. "https://github.com/orgs/<ORG>/projects/<NUMBER>"

[mnkiefer]

@copilot Fix build errors and comment whether project: value must be a quote string or just the plain url.

[Copilot]

@mnkiefer I've opened a new pull request, #12717, to work on those changes. Once the pull request is ready, I'll request review from you.

[mnkiefer]

@copilot use of this sample url was intentional 'https://github.com/orgs//projects/', make tests with it

[Copilot]

@mnkiefer I've opened a new pull request, #12720, to work on those changes. Once the pull request is ready, I'll request review from you.