[instructions] Sync github-agentic-workflows.md with undocumented features

[github-actions]

Instructions Update - Synchronized with Repository Workflows

This PR updates the github-agentic-workflows.md instructions file to include features that are already documented in the full reference documentation and actively used in repository workflows, but were missing from the concise instructions file.

Changes Made

1. Added upload-assets Safe-Output Documentation

• Publishes assets to orphaned git branch for embedding in issues, PRs, and discussions
• Configuration options: branch name, max file size, allowed extensions, max assets
• Already documented in docs/src/content/docs/reference/frontmatter-full.md

2. Added messages Configuration

• Customize workflow status messages (footer, run-started, run-success, run-failure)
• Template placeholders: {workflow_name}, {run_url}, {event_type}, {status}, {triggering_number}
• Already documented in docs/src/content/docs/reference/safe-outputs.md

3. Added serena Tool Documentation

• AI-powered code intelligence with language service integration
• Supports multiple languages: Go, TypeScript, Python, Java, Rust, C#
• Array and object configuration formats
• Already documented in docs/src/content/docs/reference/frontmatter-full.md

4. Added workflow_call Trigger Example

• Standard GitHub Actions feature for reusable workflows
• Shows how to define workflow inputs

Repository Workflows Reviewed

These features were identified by analyzing 93 workflow files in .github/workflows/, including:

• stale-repo-identifier.md (uses upload-assets, messages)
• archie.md (uses serena tool, messages)
• unbloat-docs.md (uses upload-assets, messages)
• And 15+ other workflows using these features

Documentation Commits Analyzed

• 8228e16 Convert stale repository identifier to agentic workflow (2025-12-03)

Since there are no git tags in the repository, analysis was based on current workflow usage patterns.

Validation

• Followed prompting best practices (imperative mood, minimal examples)
• Maintained technical tone and brevity
• Updated only necessary sections
• Verified accuracy against full documentation and workflow files
• Removed no content (only additions)
• All features verified in use across repository workflows

AI generated by Instructions Janitor