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

swarm-controller/src/forge.rs

@@ -267,12 +267,11 @@ impl Client {
     /// default branch — only [`OPERATORS_TEAM`] members can merge, and
     /// an approving review from that team is required, so the agent (a
     /// write-level collaborator, not in the team) cannot merge its own
-    /// PR. Mirrors `hive-c0re::forge::repos::apply_operator_branch_protection`
-    /// exactly (same policy, same verify-don't-trust shape): a create
-    /// failure is ambiguous (already-exists vs. a silent reject that
-    /// created no rule), so on any error this GETs the `main` rule and
-    /// only treats it as success if the rule is actually present — a
-    /// fail-open merge gate is a security bug, not a shrug.
+    /// PR. A create failure is ambiguous (already-exists vs. a silent
+    /// reject that created no rule), so on any error this GETs the
+    /// `main` rule and only treats it as success if the rule is
+    /// actually present — a fail-open merge gate is a security bug,
+    /// not a shrug.
     ///
     /// Also push-whitelists [`SWARM_CONTROLLER_FORGE_USER`] alone —
     /// [`Client::seed_agent_config`]'s initial commit is a direct push to