add ui, new config opts

AGENTS.md

@@ -45,6 +45,26 @@ Exporter for Rheem EcoNet / Rheemcloud water heaters, built on the
   `list_water_heaters` tool delegating to the gRPC server. Kept in place as a
   fallback. **Switch between the two** with the aliased `econetmcp` import in
   `pkg/econet/econet.go` (one line — both packages export identical symbols).
+- `pkg/econet/econetui/` — admin UI served at **`/`** (the root; the HTTP
+  server is not "under `/api`" — only the grpc-gateway is, via
+  `grpcGatewayPath`). Gated by `enableWebUI` (default true). Server-rendered
+  `html/template` + embedded assets (`embed.FS`: Pico.css classless, HTMX,
+  per-`generic_type` SVG icons) with a dark-mode toggle (persisted in
+  `localStorage`). Reads devices and writes mode through the in-process gRPC
+  server, same as the MCP packages. Routes: `GET /` (page), `GET /ui/devices`
+  (HTMX poll partial, every 30s), `POST /ui/devices/{serial}/mode` (returns a
+  re-rendered card), `GET /ui/devices/{serial}/debug` (raw device JSON for the
+  🐛 modal), `GET /static/`. A **fill-level meter** visualizes hot-water
+  availability. `iconFor` matches `@TYPE` loosely (substring, case/spacing
+  insensitive) since real values vary (e.g. `heatpumpWaterHeaterGen5`).
+  Template funcs (`fillClass`/`fillWidth`) take **int32** to match proto fields
+  — `html/template` is strict about arg types.
+  **Pending state** for a mode change is best-effort: `pending.go` holds a
+  TTL-bounded (`pendingTTL`, 90s) desired-mode hint, shown as an "Updating…"
+  badge and cleared once the reported mode converges; a full page load ignores
+  it (fresh reported state), the poll honors it. **Auth is left to the edge**
+  (oauth2-proxy) — the UI/write live at `/` and `/ui/`; keep `/health` and
+  `/metrics` on skip-auth so probes/Prometheus keep working.
 - `pkg/econet/econetmetrics/` — OTEL observable gauges (read the client
   snapshot at scrape time; no poller of its own).
 
@@ -60,6 +80,14 @@ that's all it takes — no extra wiring.
 
 - `costPerKWH` is **US dollars per kWh** (0.18 = 18¢), feeding
   `econet_energy_cost_dollars`.
+- **The `default:` tag is NOT applied at runtime for custom `ServiceConfig`
+  fields** — `LoadEnv` uses plain `env.Parse` (no `DefaultValueTagName`), so
+  `default:` only feeds the JSON schema. A bool that must default to true
+  therefore can't be a plain `bool` (zero value = false); `enableWebUI` is a
+  `*bool` where nil ⇒ enabled (read via `WebUIEnabled()`). `disableWaterUsage`
+  is a plain `bool` because its desired default (poll water usage) is the zero
+  value — set it true to skip the wasted water-usage REST call on units that
+  don't report it.
 - `econetTLSInsecure` (env `ECONET_TLS_INSECURE`) skips TLS certificate
   verification when connecting to the EcoNet cloud API. It exists because the
   upstream host (cloudblade) serves a