fix(auth): isolate server/console session cookies by name

The server (:8080) and console (:8090) both set a cookie named
`turnstone_auth`. Cookies ignore port (RFC 6265), so on a shared host
(localhost dev, the Electron build, single-box installs) logging into one
surface overwrote the other's cookie and 401'd the first session.

Give each surface its own cookie name -- `turnstone_auth_server` /
`turnstone_auth_console` -- threaded as a required `cookie_name` argument
through the cookie builders, `check_request`, `AuthMiddleware`, and the six
shared auth handlers (login/logout/setup/whoami/refresh/oidc_callback). Each
app passes its own constant; the parameter is required (no default) so a
forgotten caller fails loudly instead of silently reverting to the legacy name.

Names key on role, not node: the cluster shares one JWT identity and the
console->node proxy re-mints a bearer token (dropping Set-Cookie), so
per-instance names would break identity portability and aren't used.

Hard cutover: the legacy `turnstone_auth` cookie is no longer read and
self-expires within its 24h TTL (one forced re-login). JWT audience was
already enforced, so the shared cookie was a session clobber, not an auth
bypass.

docs/api-reference.md

@@ -63,7 +63,10 @@ Auth is always enabled. All API endpoints except public paths require a valid to
 Include a token in one of two ways:
 
 - **Bearer header**: `Authorization: Bearer <token>`
-- **Cookie**: `turnstone_auth=<token>` (set automatically by the login endpoint)
+- **Cookie**: the surface-scoped auth cookie — `turnstone_auth_server` on
+  turnstone-server, `turnstone_auth_console` on turnstone-console (set
+  automatically by the login endpoint). The names differ so the two surfaces,
+  when co-hosted on one origin, don't overwrite each other's session.
 
 The server accepts two token types:
 
@@ -102,7 +105,8 @@ Authenticate with credentials and receive a JWT. Accepts two credential formats:
 }
 ```
 
-The response also sets a `turnstone_auth` HttpOnly cookie containing the JWT.
+The response also sets a surface-scoped HttpOnly cookie containing the JWT
+(`turnstone_auth_server` on turnstone-server, `turnstone_auth_console` on turnstone-console).
 
 **Response (failure):** `401`
 
@@ -114,7 +118,8 @@ The response also sets a `turnstone_auth` HttpOnly cookie containing the JWT.
 
 ### `POST /v1/api/auth/logout`
 
-Clears the `turnstone_auth` cookie. No request body required.
+Clears the surface-scoped auth cookie (`turnstone_auth_server` /
+`turnstone_auth_console`). No request body required.
 
 **Response:** `200`
 
@@ -199,7 +204,8 @@ this endpoint.
 }
 ```
 
-The response also sets a `turnstone_auth` HttpOnly cookie containing the JWT.
+The response also sets a surface-scoped HttpOnly cookie containing the JWT
+(`turnstone_auth_server` on turnstone-server, `turnstone_auth_console` on turnstone-console).
 
 **Response (already set up):** `409`