Fix gh aw init staging guidance in terminal install steps

[Copilot]

workshop/06a-install-terminal.md instructed learners to stage only .github/skills/agentic-workflows/ after gh aw init, even though current gh-aw generates additional required files. Following the step verbatim could leave repos partially initialized and break later workflow setup.

• Scope

  • Update both terminal-path install steps:
    • workshop/06a-install-terminal.md
    • workshop/06b-install-local.md

• Instruction fix

  • Replace the partial staging command with an explicit add covering all generated paths:

    gh aw init
    git add .github/ .gitattributes .vscode/
    git commit -m "Initialize agentic workflow skills"
    git push

• Generated file explanation

  • Expand the prose after gh aw init to reflect the actual outputs, including:
    • skill files under .github/skills/
    • custom agent definition under .github/agents/
    • MCP config in .github/mcp.json
    • Copilot setup steps in .github/workflows/copilot-setup-steps.yml
    • editor settings in .vscode/
    • .gitattributes

• Checkpoint alignment

  • Update the checkpoint text from committing only agentic-workflows skill files to committing all files generated by gh aw init.