Summary

Modernize repository documentation to reflect current GitHub Copilot UI pattern where agents are selected from agent picker dropdown rather than using deprecated @mention syntax.

Background

GitHub Copilot UI evolved from @agent-name mention syntax to agent picker dropdown selection. Repository documentation still references old @mention pattern, causing user confusion and mismatched instructions.

Objectives

• Replace all @agent-name mentions with agent picker dropdown instructions
• Update verification/troubleshooting steps to match current UI
• Provide consistent user guidance across all documentation
• Fix table formatting issues discovered during review

Changes

.github/chatmodes/README.md

• Replace @prompt-builder references with "select prompt-builder from agent picker dropdown"
• Update "Recommended Approach" section to use picker instructions
• Maintain bold formatting for agent names

.github/instructions/README.md

• Replace @prompt-builder with "prompt-builder agent" or dropdown instructions
• Update "How Instructions Work" and "Creating Instructions Files" sections
• Clarify that agents are selected from picker, not mentioned

README.md

• Remove: Code block with @agent-name examples
• Add: Numbered steps for using agent picker dropdown:
  1. Open Chat view (Ctrl+Alt+I)
  2. Click agent picker dropdown
  3. Select desired agent (task-planner, task-researcher, prompt-builder, pr-review)
• Provide keyboard shortcut and clear navigation

docs/getting-started.md

• Update "Verifying Setup" section with agent picker instructions
• Add troubleshooting guidance for agent discovery issues
• Reference chat.modeFilesLocations setting for configuration

SUPPORT.md

• Fix table formatting (align separator row with headers)
• No content changes, only markdown quality improvement

Acceptance Criteria

• All @mention syntax replaced with agent picker instructions
• Verification steps updated to match current UI
• Consistent terminology across all files ("agent picker dropdown")
• All files pass npm run lint:md
• Table formatting correct in SUPPORT.md
• No broken cross-references

Technical Notes

• UI Pattern: Agent picker dropdown is accessed at top of Copilot Chat panel
• Agent Names: Use bold formatting when referencing agents: prompt-builder
• Keyboard Shortcut: Ctrl+Alt+I opens Copilot Chat view
• Troubleshooting: Reference chat.modeFilesLocations setting if agents don't appear

Testing

Verify instructions match actual GitHub Copilot behavior:

1. Open Copilot Chat (Ctrl+Alt+I)
2. Click dropdown at top of chat panel
3. Confirm custom agents appear (task-planner, task-researcher, prompt-builder, pr-review)
4. Select an agent and verify behavior matches documentation

Related Issues

Part of AI artifact contribution documentation initiative (PR feat/ai-artifact-contrib-docs)