refactor(server): lift close handler into shared session_routes body

Stage 2 Priority 0 Step 0.2 body-convergence — second verb.
``make_close_handler(audit_emit=..., supports_close_reason=...)``
factory in ``turnstone/core/session_routes.py`` produces the lifted
body; both interactive and coord pass their kind-specific audit
emitter at app construction.

The two body-keyed close URL aliases on the interactive side reach
the same lifted body:

- ``POST /v1/api/workstreams/{ws_id}/close`` (new, path-keyed)
  via ``register_session_routes(handlers.close=...)``.
- ``POST /v1/api/workstreams/close`` (legacy, body-keyed) via
  ``make_legacy_body_keyed_adapter(close_handler)``.

Coord exposes only the path-keyed shape.

Behavior gains:

- ``supports_close_reason=True`` (interactive only) keeps the 512-
  byte UTF-8 cap + credential redaction + ``workstream_config``
  persistence path. Coord stays at ``False``; if coord ever wants
  close-reason metadata, flipping the flag is a one-line change.
- ``audit_emit`` is per-kind so each owns its detail dict shape
  (``{kind, parent_ws_id, reason}`` vs ``{coord_ws_id, src}``) and
  audit action name (``workstream.closed`` vs ``coordinator.close``).
- Standardizes the close-failure status code to 404 across both
  kinds. The coord code previously returned 500 on a
  ``mgr.close()`` race-loss, which was overly pessimistic — the
  semantic is "the ws was popped between .get() and .close()", i.e.
  not-found.

Coord-side test fixtures (``test_coordinator_endpoints``,
``test_coordinator_end_to_end``) swap the imported
``coordinator_close`` for the lifted handler + a local audit_emit
adapter so the tests exercise the same code path the live console
does.

ruff + mypy + 4366 pytest pass. Live console smoke against
``POST /v1/api/workstreams/abc/close`` returns 503 (no coord_mgr
loaded in the smoke env) — proves the lifted handler is reachable
+ the manager_lookup callable fires correctly.

Two verbs converged so far (``approve`` + ``close``); the remaining
pairs (``send``, ``cancel``, ``open``, ``events``, ``create``,
``list``, ``saved``, ``history``, ``detail``) have substantive
behavior divergence that doesn't factor cleanly into the
SessionEndpointConfig + factory-handler pattern — see the
session_routes module docstring for the per-verb status.

tests/test_coordinator_endpoints.py

@@ -8,6 +8,7 @@ enforcement, and lazy rehydration on GET /{ws_id}.
 
 from __future__ import annotations
 
+from typing import TYPE_CHECKING
 from unittest.mock import MagicMock
 
 import httpx
@@ -28,12 +29,12 @@ from tests._coord_test_helpers import (
 )
 from turnstone.console.coordinator_ui import ConsoleCoordinatorUI
 from turnstone.console.server import (
+    _auth_user_id,
     _require_admin_coordinator,
     _require_coord_mgr,
     cluster_ws_detail,
     coordinator_cancel,
     coordinator_children,
-    coordinator_close,
     coordinator_create,
     coordinator_detail,
     coordinator_history,
@@ -43,10 +44,37 @@ from turnstone.console.server import (
     coordinator_send,
     coordinator_tasks,
 )
+from turnstone.core.audit import record_audit
 from turnstone.core.auth import AuthResult
-from turnstone.core.session_routes import SessionEndpointConfig, make_approve_handler
+from turnstone.core.session_routes import (
+    SessionEndpointConfig,
+    make_approve_handler,
+    make_close_handler,
+)
 from turnstone.core.storage._sqlite import SQLiteBackend
 
+if TYPE_CHECKING:
+    from turnstone.core.workstream import Workstream
+
+
+def _audit_close_coordinator_for_test(
+    request,
+    ws_id: str,
+    ws_before: Workstream,  # noqa: ARG001
+    reason: str,  # noqa: ARG001
+) -> None:
+    storage = request.app.state.auth_storage
+    record_audit(
+        storage,
+        _auth_user_id(request),
+        "coordinator.close",
+        "workstream",
+        ws_id,
+        {"coord_ws_id": ws_id, "src": "coordinator"},
+        request.client.host if request.client else "",
+    )
+
+
 # ---------------------------------------------------------------------------
 # Fixtures
 # ---------------------------------------------------------------------------
@@ -97,7 +125,10 @@ def _make_client(
             ),
             Route(
                 "/v1/api/workstreams/{ws_id}/close",
-                coordinator_close,
+                make_close_handler(
+                    audit_emit=_audit_close_coordinator_for_test,
+                    supports_close_reason=False,
+                ),
                 methods=["POST"],
             ),
             Route(