bug: create-agent-session fails with fine-grained PATs

[microsasa]

The create-agent-session safe output in gh-aw uses gh agent-task create which requires OAuth authentication. Fine-grained PATs (used for COPILOT_GITHUB_TOKEN) produce:

this command requires an OAuth token. Re-authenticate with: gh auth login

This breaks the automated chain where code-health and test-audit agents create issues and then trigger implementation.

Fix: replace create-agent-session with dispatch-workflow pattern using a dedicated issue-implementer workflow.