feat(devices): radar presence input + button-light output on the controller

Model the entry button (I1) and a Hikvision radar (I2) as named children of the
access controller, and drive the button's 12V lamp on a spare relay.

- Radar = the existing relays[].presenceInput one-car-one-ticket gate, now labelled
  presenceKind: loop|radar. A radar may idle opposite the button, so add a per-input
  active-level override: relays[].presenceActiveLow -> driver inputActiveLow set,
  inverting just that terminal (pure helper inputActive()). The Dingtian has one
  board-wide resting level otherwise.
- AuxOutputDevice.setAux(channel,on) capability on the device interface (Dingtian
  latch) so business logic drives a NON-barrier lamp through the interface. Barriers
  still only pulseOpen — barrier-not-a-door preserved.
- ButtonLightController: subscribes to the radar input edge + the camera lane status
  and drives a 3-state lamp — radar+car=solid, radar-only=blink (~1Hz), else off.
  Fails OFF on host loss/error; de-duped. A radar detection never opens a barrier on
  its own (advisory; threat model).
- SetupWizard: presence kind + active-low + a button-light relay picker; sq+en i18n.

Tests: button-light.test.ts (truth table + blink + fail-OFF + de-dupe),
access-dingtian.test.ts (active-level inversion). Workspace build+lint+test green
(158 server tests). Wiki: hikvision-radar, button-light-indicator + updates.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

wiki/concepts/button-light-indicator.md

@@ -0,0 +1,62 @@
+---
+type: concept
+tags: [parking, device, indicator, radar, camera, aux-output, barrier-not-a-door]
+sources: []
+updated: 2026-06-24
+status: settled
+---
+
+# Button-light indicator (radar × camera disagreement lamp)
+
+The entry button has a **12 V light**. It is driven by the host on a **spare relay** of the
+[[dingtian-relay|Dingtian]] controller as a 3-state indicator that combines the **[[hikvision-radar|
+radar]]** input with the **camera "car in zone"** signal:
+
+| Radar input | Camera (lane entry busy) | Button light |
+| --- | --- | --- |
+| detecting | **free** — no car confirmed | **BLINK** (~1 Hz) |
+| detecting | **busy** — camera confirms a car | **SOLID on** |
+| clear | — | **OFF** |
+
+It is a **disagreement indicator**: the radar sees *something* but the camera hasn't confirmed a
+real vehicle → blink (attention / "pull forward"); both agree → solid; nothing there → off.
+
+## Signals
+
+- **Radar** = the presence input edge on the entry relay (`relays[].presenceInput`, the same edge
+  the [[entry-double-press|one-car-one-ticket]] gate observes — so the lamp and the gate always
+  agree on "a car is here").
+- **Camera "car in zone"** = the existing **[[lpr-camera|lane status]]** (`LaneStatusEvent` entry
+  busy/free, from camera vehicle detection). Already advisory; already drives the booth's barrier
+  lights. No new camera plumbing.
+
+## Config
+
+A controller-level `config.buttonLight = { relay, blinkOnMs?, blinkOffMs? }` (the operator picks a
+**spare** relay — not a barrier relay; the setup UI warns if it overlaps one). Blink defaults to
+500 ms / 500 ms.
+
+## Implementation
+
+`apps/server/src/button-light.ts` — `ButtonLightController` subscribes to `deviceEvents.onInput`
+(radar) + `onLaneStatus` (camera), computes the target state per controller, and drives the lamp via
+a **device-agnostic aux-output** capability.
+
+- **Aux-output capability.** `AuxOutputDevice { setAux(channel, on) }` on the device interface (the
+  Dingtian driver implements it as a latch). Business logic drives the lamp through this — **never**
+  the driver's barrier methods.
+- **Barrier-not-a-door is preserved.** The lamp is **not a barrier**, so holding / blinking it on a
+  timer is fine — the [[barrier-not-a-door]] rule forbids timing a *barrier* closed, and barriers
+  still only ever `pulseOpen`. The lamp uses the separate `setAux` latch.
+- **Fails OFF.** On host loss, shutdown, or a `setAux` error the lamp defaults OFF — a dead lamp is
+  "no hint", never a misleading solid "go". SOLID is only ever held while busy + present is actively
+  true (never latched on through a crash path).
+- **De-duped.** Only writes when the effective output changes, so the 50 ms input poll doesn't spam
+  the controller over UDP.
+
+## Status
+
+Built 2026-06-24 for the first booth (button I1, radar I2, lamp on a spare relay). Covered by
+`apps/server/src/button-light.test.ts` (the truth table + blink toggling + fail-OFF + de-dupe).
+Related: [[hikvision-radar]], [[entry-double-press]], [[lpr-camera]], [[dingtian-relay]],
+[[barrier-not-a-door]].