Replace the dashboard's 5s polling with a Server-Sent Events stream:
- StatusHandle gains a tokio `watch` version bumped on every mutation;
GET /admin/crawler/stream subscribes and pushes a composed snapshot
immediately on connect, then on every status change (instant, no
lost-wakeup) plus a 5s backstop for DB queue counts / browser phase.
- Non-status signals poke the notifier so they push immediately too:
session-expired (worker), session update / clear-expired / browser
restart (endpoints).
- compose_status is shared by the one-shot GET and the stream; the stream
tolerates transient DB errors with a keep-alive comment instead of
tearing down.
Frontend: the crawler page opens an EventSource on mount and closes it on
destroy, so the subscription is scoped to the active page (no global
subscription). A one-shot fetch still paints initial state / serves as a
fallback if SSE is blocked; a live/reconnecting indicator reflects the
connection. The existing reverse proxy already streams SSE (its abort
timer is cleared once response headers arrive), so no proxy change needed.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
da6e320836