[plan] Add fork support documentation page

[github-actions]

Context

Closes part of #18481 — gh-aw in forks.

There is currently no documentation explaining how gh-aw behaves in forked repositories, what works, what doesn't, and how to set things up correctly.

Objective

Add a documentation page on fork support under docs/ covering the compatibility matrix, required setup steps for fork users, and explanation of design decisions.

Approach

1. Create a new documentation page, e.g., docs/src/content/docs/guides/fork-support.md (follow the existing Diátaxis/Starlight conventions used in docs/).

2. The page should include:

   • Overview: two fork scenarios (inbound fork PRs vs. running gh-aw in a fork)

   • Compatibility table (based on the scout report):

     Feature	Status in Fork	Notes
     pull_request fork filtering	✅ Works	Compiler injects repo ID check
     workflow_run cross-fork safety	✅ Works	Fork check injected at compile time
     Running your own workflows	⚠️ Partial	Must configure own secrets
     Agentic maintenance	⚠️ Skipped	Fork detection added; skips gracefully
     Slash commands	⚠️ Partial	Works if secrets configured
     Secrets	❌ Not inherited	Must reconfigure in fork settings

   • Setup guide: step-by-step for configuring required secrets in a fork

   • forks: frontmatter field: explanation of allow-listing trusted forks

   • Known limitations: features that won't work regardless of secret setup

3. Reference the documentation skill (skills/documentation.md) for style/format guidelines.

4. Verify the page renders correctly in the docs site structure.

Files to Create/Modify

• docs/src/content/docs/guides/fork-support.md (new)
• Possibly update docs/src/content/docs/guides/ index or sidebar config

Acceptance Criteria

• New documentation page exists covering the two fork scenarios
• Compatibility table present with accurate status
• Setup guide covers all required secrets
• forks: frontmatter field documented
• Page follows existing docs style and Diátaxis conventions
  Related to Using gh-aw in forks of repositories #18481

Generated by Plan Command for issue #18481

• expires on Feb 28, 2026, 4:18 PM UTC

[pelikhan]

@copilot forks are not supported. Agentic Workflows will try to cancel all actions but they will not run agents.