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-core-agent-sock/src/lib.rs

@@ -83,13 +83,6 @@ pub enum Request {
     /// per-kind semantics in
     /// `docs/process/conventions.md::Loose-ends wire shape`.
     CancelLooseEnd { kind: CancelLooseEndKind, id: i64 },
-    /// Create a git repo *through hive-c0re*. Agents can't create
-    /// repos with their own forge token (`max_repo_creation = 0`); this is
-    /// the sanctioned path. hive-c0re creates `repo` in the c0re-owned
-    /// `agents` org, adds the calling agent as a write collaborator (not
-    /// owner), and applies operator-team branch protection so the author
-    /// can't merge its own PRs. Returns the new repo's full name.
-    CreateRepo { repo: String },
     /// Mark every message popped since the last `AckTurn` as handled.
     /// Harness↔broker pairing fired after `TurnOutcome::Ok`. See
     /// `docs/process/conventions.md::Broker delivery + ack cycle`.
@@ -222,12 +215,6 @@ pub enum Response {
     /// authorized to see — see `ListSchedules`'s own doc comment.
     /// Returned on the manager socket only.
     Schedules { schedules: Vec<WireSchedule> },
-    /// `CreateRepo` result: the new repo's full name (`agents/<repo>`)
-    /// and clone URL, so the agent can immediately `git clone` it.
-    RepoCreated {
-        full_name: String,
-        clone_url: String,
-    },
     /// `Recv` result when a graceful stop is pending for this agent
     /// (set by hive-c0re's `GracefulStop` orchestration). Returned in
     /// place of `Messages` — it doubles as the inbound fence: the harness