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-agent-mcp/src/mcp/args.rs

@@ -103,13 +103,6 @@ pub struct SetStatusArgs {
     pub text: String,
 }
 
-#[derive(Debug, serde::Deserialize, schemars::JsonSchema)]
-pub struct CreateRepoArgs {
-    /// Repo name — a single segment of letters, digits, `-`, `_`, `.`
-    /// (no leading `-`/`.`). The repo is created as `agents/<repo>`.
-    pub repo: String,
-}
-
 #[derive(Debug, serde::Deserialize, schemars::JsonSchema)]
 pub struct GetAgentMetaArgs {
     /// Logical name of the agent to query (e.g. `"iris"`, `"manager"`).