Allow integration installs to complete from a CLI

The API-mode integration pipeline (POST /api/0/organizations/{org}/pipeline/integration_pipeline/) already models most providers as API steps, but a client authenticated with a bearer token (e.g. the Sentry CLI, getsentry/toolkit#1519, getsentry/toolkit#1520) can't finish an install. Blockers • State is session-bound. RedisSessionStore keys pipeline state via request.session (src/sentry/utils/session_store.py), and Pipeline.get_for_request / unpack_state read it from there (src/sentry/pipeline/base.py). Token requests have no session, so nothing persists between initialize and later steps. • OAuth callbacks only reach a browser. PipelineAdvancerView (src/sentry/web/frontend/pipeline_advancer.py, extensions/<provider>/setup/) looks up the pipeline from the browser's session and, in API mode, relays params to window.opener via postMessage. A pipeline started by a CLI is never found ("Invalid request"). • OAuth state is not per-pipeline. pipel…