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

hive-c0re/src/forge/users.rs

@@ -208,10 +208,9 @@ pub(super) async fn ensure_user_email(name: &str) {
 }
 
 /// Disable direct repo creation for agent `name` by setting
-/// `max_repo_creation = 0` on its Forgejo account. Agents must
-/// create repos *through hive-c0re* (which owns the perms), never with
-/// their own token — a write-scoped token can otherwise create + own
-/// repos and self-merge, bypassing the operator-only-merge policy.
+/// `max_repo_creation = 0` on its Forgejo account. A write-scoped token
+/// can otherwise create + own repos and self-merge, bypassing the
+/// operator-only-merge policy.
 ///
 /// `max_repo_creation = 0` means `CanCreateRepo()` is false for any
 /// count (Forgejo: `MaxRepoCreation >= 0 && NumRepos >= MaxRepoCreation`),