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/turn-loop/mcp.md

@@ -137,13 +137,8 @@ hive_name?, swarm_name?, matrix_accounts? }`. `matrix_accounts` is a
   [`docs/agent-lifecycle/approvals.md`](../agent-lifecycle/approvals.md).
 - **Scheduling** (`scheduling`) — scheduled prompts. See
   [`docs/tools/scheduling.md`](../tools/scheduling.md).
-- **Forge repos** (`forge`) — `create_repo` — the only agent path to
-  create a repo under the `agents/` org (direct forge token creation is
-  disabled for agents). The repo lands in the c0re-owned `agents`
-  org; the calling agent gets write collaborator access; the default
-  branch is branch-protected (operator-team must approve merges, so the
-  agent can't self-merge). Opt-in; not in any default preset.
-  See [`docs/tools/forge.md — Repo management`](../tools/forge.md).
+- **Forge repos** (`forge`) — carries no MCP tool: `create_repo` no
+  longer exists, with no replacement; `forge` gates nothing.
 - **Web egress** (`web_tools`) — enables Claude's built-in `WebFetch`
   and `WebSearch` tools (not MCP tools; added directly to the
   `--allowedTools` list). Off by default; add the group in the