docs(#2999): document the takeover process for a capability, reviewer lane, or EoS integration (#3000)

* docs(#2999): document the capability / reviewer-lane / EoS takeover process

The capability ecosystem documented a complete forward lifecycle — develop,
publish, version, import, update, remove, turn off — but nothing covering a
change of maintainer for an entry that already exists. Adds
docs/how-to/take-over-a-capability-or-eos.md defining four takeover modes
(consensual handoff, adoption fork, first-party absorption, retirement), the
PR shape each takes, a per-surface snapshot of the inherited user-visible
contract, and an install-continuity checklist.

Also corrects .github/PULL_REQUEST_TEMPLATE/registry-entry.md, which directed
contributors to a 'Registry' Discussions category that does not exist — the
category is named 'EoS Registry' per docs/registries/README.md, and because
'discussion' is a required field the thread must exist before the PR is
opened, so the wrong name stalled contributors at the first required step.

Closes #2999

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* chore(#2999): backfill changeset pr number to 3000

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

---------

Co-authored-by: sim <sim@local>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

docs/README.md

@@ -38,6 +38,7 @@ Language versions: [English](README.md) · [Português (pt-BR)](pt-BR/README.md)
 - [Develop a Capability for GSD 1.5+](how-to/develop-a-capability.md) — add feature Capabilities, hook fragments, and registry entries
 - [Ship a reviewer lane in your capability](how-to/ship-a-reviewer-lane.md) — declare a `reviewer` body so `/gsd-review` discovers, invokes, and renders your external review CLI or model endpoint
 - [List your reviewer lane in the registry](how-to/list-your-reviewer-lane.md) — publish a lane you have built to the Reviewer Lane Registry so other people can find and install it
+- [Take over a capability or EoS integration](how-to/take-over-a-capability-or-eos.md) — assume maintainership of an existing third-party capability, reviewer lane, or EoS host integration through a handoff, an adoption fork, first-party absorption, or a de-listing
 - [Add or update a host's integration](how-to/add-or-update-a-host-integration.md) — set a host's documentation-sourced `runtime.hostIntegration` axes (ADR-1239 Phase A), with the `undocumented` sentinel rule
 - [Turn a capability off (and keep it off)](how-to/turn-a-capability-off.md) — disable a capability via the surface, or gate individual hooks off without removing the capability
 - [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