phase 6: container events + drop the 5s /api/state poll

new DashboardEvent::ContainerStateChanged + ContainerRemoved
close the last refetch loop on the dashboard. Coordinator's
rescan_containers_and_emit diffs a fresh container_view::build_all
against a cached last_containers map and fires per-row events.
called from actions::approve (post-spawn), actions::destroy,
the lifecycle_action wrapper, auto_update::rebuild_agent, and
the existing 10s crash_watch poll.

ContainerView extracted to its own module so coordinator and
dashboard can both build it. dashboard endpoints flip to 200;
container-lifecycle forms carry data-no-refresh. client drops
the periodic poll entirely — initial cold load + SSE for
everything afterwards. pending overlay reads from the existing
transientsState since the new event payload doesn't carry it.

PURG3 + meta-update keep the post-submit refetch since
tombstones + meta_inputs aren't event-derived yet; tracked in
TODO.md.

CLAUDE.md

@@ -193,6 +193,26 @@ Prune freely.
   domain tooling — the agent flake's `inputs` block pulls
   the external flake, `agent.nix` references it via
   `flakeInputs.<name>.packages.${pkgs.system}.default`.
+- **Just landed:** Phase 6 container events. New
+  `DashboardEvent::ContainerStateChanged { container }` +
+  `ContainerRemoved { name }` close the last refetch loop on the
+  dashboard side. `Coordinator::rescan_containers_and_emit` builds a
+  fresh `container_view::build_all` snapshot, diffs it against a
+  cached `last_containers` map, and fires per-row events for the
+  delta. Called from every mutation site: `actions::approve`
+  (post-spawn), `actions::destroy`, the `lifecycle_action` wrapper
+  in `dashboard.rs` (start/stop/restart/rebuild), `auto_update::
+  rebuild_agent`, and the existing 10s `crash_watch` poll loop.
+  `ContainerView` extracted to its own module so coordinator +
+  dashboard can both build it. Dashboard endpoints (`/restart`,
+  `/destroy`, `/kill`, `/rebuild`, `/start`, `/update-all`,
+  `/meta-update`, `/purge-tombstone`) now return 200; matching
+  forms carry `data-no-refresh` where the event coverage is
+  complete (purge + meta-update keep the refetch since tombstones
+  + meta_inputs aren't event-derived yet). Client drops the 5s
+  periodic `/api/state` poll entirely — initial cold load + SSE
+  for everything afterwards; pending overlay reads from
+  `transientsState` since the new event payload doesn't carry it.
 - **Just landed:** dashboard event refactor. New `hive-fr0nt`
   workspace crate hosts shared frontend assets (palette + terminal
   CSS + `window.HiveTerminal.create` JS) so both the dashboard and