chore(agents): reorganize agent instructions into data/ subdirectory (#193)

Reorganize .github/agents/ to extract repo-specific context into data/ files consumed by named agents. Delete 5 legacy inline-context agent files, add 5 structured data files.

- holiday-peak-hub.yaml (The Architect)
- holiday-peak-hub-specs.md (The Architect — impl specs #79-#84)
- holiday-peak-hub-connectors.yaml (The Patchbay)
- holiday-peak-hub-platform.yaml (The Quartermaster)
- holiday-peak-hub-pr-review.md (The Gatekeeper)

Architecture sign-off: approved. No production code, CI, or infra changes.

Closes #193

Author: Cataldir