The full switch: Monitors and Disks read only the sensor API; /api/metrics retired

- stock Monitors modules fed by one sensor stream, the catalog and one batch of
  histories (GET /api/sensors/history?ids=…), through sampleAdapter.ts
- the stream closes while the page is hidden and refills its curves on return
- Disks tab live rates from the stream
- new sensors: hamlab.sample_interval, ups.last_event
- stream: asking for about the sampling rate means every sample
- NUT runtime rounded at the source

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

PLAN.md

@@ -166,8 +166,8 @@ something long in one, switch away and back, refresh — it's all still there.
   CPU (total + per core), memory/swap, load, uptime, hwmon temps and fans read straight
   from `/sys` (no lm-sensors), per-interface network rates, per-disk read/write/busy
   from `/proc/diskstats`, filesystem usage, UPS via `sudo -n pwrstat -status`. Sampled
-  every 2 s into an in-memory ring of 10 min; the UI seeds from
-  `GET /api/metrics/history` then polls `GET /api/metrics`. **Customizable**: a
+  every 2 s into an in-memory ring of 10 min; the UI (the **Monitors** tab
+  since 2026-09-19) reads it all through the sensor API — see Sensors below. **Customizable**: a
   Customize mode reorders and hides modules (CPU, Memory, Load, Uptime, Temperatures,
   Fans, Network, Disks, Filesystems, UPS) and hides individual rows (an interface, a
   mount, a disk, a sensor); the layout is stored server-side in `state.json` via
@@ -185,8 +185,9 @@ something long in one, switch away and back, refresh — it's all still there.
   SSE stream, Prometheus `/metrics`, read-only `sensors:read` tokens (never full tokens in
   a URL), status sensors (services, updates, ZFS, SMART), a widget library, custom widgets
   on the Monitors tab (was "Dashboard"; the view id and URL are still `dashboard`), and a
-  frameable `/embed/widget` for Glance and friends. **Remaining:** port the stock Monitors
-  modules onto sensors; per-unit service and container sensors; pattern-restricted tokens;
+  frameable `/embed/widget` for Glance and friends. The stock Monitors modules and the Disks
+  tab read the sensor API too (`sampleAdapter.ts`); `/api/metrics` is retired.
+  **Remaining:** per-unit service and container sensors; pattern-restricted tokens;
   one-request fleet query.
 - **Multi-host** — **Phase 1 shipped 2026-09-18** (`internal/nodes`, `internal/tlsauto`,
   `MachineSwitcher.tsx`, `Machines.tsx`). One binary, hub and spoke: a host whose