feat(#1135): migrate planning hooks to capabilities (#1141)

* feat(#1135): migrate planning hooks to capabilities

* chore(#1135): add phase 6 planning capabilities changeset

* fix(#1135): satisfy lint for agent hook rendering

docs/README.md

@@ -31,6 +31,7 @@ Language versions: [English](README.md) · [Português (pt-BR)](pt-BR/README.md)
 - [Debug a failed execution](how-to/debug-a-failed-execution.md) — diagnose and recover from broken or incomplete phase execution
 - [Spike and sketch](how-to/spike-and-sketch.md) — use `/gsd-spike` and `/gsd-sketch` for exploratory work before committing to a plan
 - [Design a UI phase](how-to/design-a-ui-phase.md) — use the UI phase loop for frontend and visual work
+- [Develop a Capability for GSD 1.5+](how-to/develop-a-capability.md) — add feature Capabilities, hook fragments, and registry entries
 - [Drive GSD from a tracker issue](how-to/drive-gsd-from-a-tracker-issue.md) — start a phase from a GitHub, Linear, or Jira issue
 - [Migrate from GSD 2](how-to/migrate-from-gsd-2.md) — upgrade an existing GSD 2 project to GSD Core
 - [Update GSD](how-to/update-gsd.md) — re-run the installer to pick up the latest release