wip: snapshot live progress, universal --init, runner perms, supervisord SIGINT

- Snapshot detail page: embed scoped live-progress monitor (same-origin
  /progress.json on whichever host the page is served from); hide admin
  action buttons when scoped; per-snapshot perms via can_view_snapshot.
- crawl_file API: respect crawl-level permissions; PUBLIC/UNLISTED served
  to guests, PRIVATE returns 404 for non-admin/non-owner.
- CrawlRunner: replace allow_paused_snapshot_maintenance with
  allow_maintenance_on_inactive_crawl so SEALED crawls don't short-circuit
  the cancellation guard for legitimate maintenance hooks (search backend
  backfill, fs migration, etc.). Fixes infinite STARTED loop on snapshots
  with queued search_backend results.
- Universal `--init` flag: works on any subcommand (server, update, add,
  shell, install, ...). Detected at module load, stripped from argv, and
  consumed in the dispatcher so subprocesses inherit a clean env.
- supervisord_util.run_runner_worker: route Ctrl+C through
  supervisor.signalProcess(name, "SIGINT") instead of raw os.kill on a
  cached pid, gated on statename=RUNNING. Prevents killing unrelated
  processes when the worker's pid has been reused by the OS.
- Login page: remove non-functional password-reset links; add
  has_real_admin_users template tag to gate the bootstrap hint.
- Add page: hide underline on the "Get the extension" link.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>