remove the create_repo agent tool

mara ruled on #4849 (c88934): "remove create_repo tool". The tool ran in
hive-c0re with the hive's core token, so it only ever worked for agents
on the hive that runs the forge.

Removed:

- the create_repo MCP tool and CreateRepoArgs (hive-agent-mcp)
- wire variants Request::CreateRepo and Response::RepoCreated
  (hive-core-agent-sock)
- hive-c0re's handle_create_repo, its valid_repo_name check and the
  dispatch arm
- forge::create_agent_repo and apply_operator_branch_protection, which
  had no other caller, plus AGENTS_ORG and OPERATORS_TEAM, whose only
  users they were
- the tool's docs (docs/tools/forge.md repo management, docs/turn-loop/
  mcp.md, the conventions tool-group table) and the doc comments that
  named it (hive-sock-client's response timeout, ensure_repo_creation_
  disabled, the security doc's merge-gate bullet)

ToolGroup::Forge is kept with no tools, the same way b88a5b24 kept
Lifecycle, so existing meta/capabilities.json grants still parse.

Forge state is untouched: existing agents/* repos keep their collaborators
and operators-team branch protection. The swarm-controller's own
create_repo (config-org repos) is a different path and is unchanged.

Closes #4849

docs/tools/forge.md

@@ -212,18 +212,11 @@ plain comment show under `last comment`, not `reviews`.
 
 Agents **can't create repos directly via forge token** — Forgejo
 disables push-to-create and the agent token doesn't have the Create
-scope. Two paths exist depending on where the repo should live:
+scope.
 
-**Agent repos (`agents/<name>`)** — Use the `mcp__hyperhive__create_repo`
-MCP tool (requires the `forge` tool group). hive-c0re creates the repo in
-the c0re-owned `agents/` org, adds you as a write collaborator (not
-owner), enables branch protection (operator-team merge approval
-required — you can't self-merge), and returns the clone URL immediately.
-This is the standard path for agents that need a working repo.
-
-**Other repos** — Use the CLI verbs below (`repo-create` / `repo-add-collaborator`).
-These use the agent's own forge token so the repo lands under the agent's
-user account or an org the agent belongs to.
+The CLI verbs below (`repo-create` / `repo-add-collaborator`) use the
+agent's own forge token, so a repo lands under the agent's user account
+or an org the agent belongs to.
 
 **`repo-create <name>`** — create a repo under the authenticated user
 and print its URL. Key flags: