Delegate releases to Standards

[lipkau]

Summary

• Delegate releases to the reusable AtlassianPS.Standards v0.1.16 workflow, pinned to commit 3c050eda17bfb4177f93c3cac61610a6f21b2537.
• Build one secretless candidate artifact, then stamp and verify that same artifact for release PRs.
• Test the artifact on Windows PowerShell 5.1, PowerShell 7, Ubuntu, and macOS while preserving Confluence-specific smoke tests.
• Add release-intent validation, Dependabot labels, workflow contract tests, and ConfluencePS release documentation.
• Remove repository-owned publishing and the copied tag-driven release workflow.

Release behavior

• A merged release:* label and changelog fragment drive the next version.
• Standards opens Prepare vX.Y.Z release.
• CI stamps and verifies the candidate only on that release PR.
• The shared workflow publishes the tested ZIP to PowerShell Gallery and GitHub Releases, creates the annotated tag, and opens the homepage update.

This PR is labeled release:patch and changelog:changed, so merging it should produce the v2.5.1 release.

Validation

• actionlint .github/workflows/*.yml
• 9 focused workflow and Standards consistency tests
• Invoke-Build -Task Lint, Build, Test — 180 tests passed
• Real v2.5.1 local rehearsal through changelog preparation, source-version stamping, artifact build/stamping, ZIP validation, and embedded release notes
• Exact planner dry-run against current master; all historical changes classified
• Independent review: no critical or important findings