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/process/conventions.md

@@ -302,7 +302,7 @@ binary flavor.
 | `lifecycle` | none — `list_containers` no longer exists, with no replacement; the variant survives only so existing grants parse. |
 | `approvals` | none — `request_update_meta_inputs` no longer exists, with no replacement. Still a live server-side gate: `cancel_loose_end`'s approval-cancel arm requires it. |
 | `scheduling` | `request_schedule_prompt`, `fire_schedule_now`, `cancel_schedule`, `edit_schedule`, `list_schedules` *(privileged)* |
-| `forge` | `create_repo` — create git repos through hive-c0re (operator-gated merge) |
+| `forge` | none — `create_repo` no longer exists, with no replacement; the variant survives only so existing grants parse. |
 | `web_tools` | none (gates the Claude built-ins `WebFetch`/`WebSearch`, not an MCP tool) |
 
 **Always-on tools** — `ToolGroup::ALWAYS_ON_TOOLS` exposes `set_status`,