chore(github): enforce agent-generated issue intake templates

[Copilot]

Summary

This updates GitHub issue intake so humans are directed to file issues via an agent, and only submissions generated with the ado-aw agent file are accepted through the default form.

• Issue intake gating
  • Added .github/ISSUE_TEMPLATE/config.yml with blank_issues_enabled: false.
  • Added a contact link pointing contributors to .github/agents/ado-aw.agent.md and the agent-only filing requirement.
• Agent-only issue form
  • Added .github/ISSUE_TEMPLATE/agent-generated-issue.yml.
  • Requires submitter confirmation that the issue was generated by an agent using .github/agents/ado-aw.agent.md.
  • Requires structured generated content (problem summary, repro details, proposed next step) for triage quality.

blank_issues_enabled: false
contact_links:
  - name: Issues must be generated by an agent
    url: https://github.com/githubnext/ado-aw/blob/main/.github/agents/ado-aw.agent.md

Test plan

N/A — repository metadata/template-only change.