discovery: generate capability JSON from the registry

A capability is a descriptor plus what the endpoint declares (device/Capability.ts), and its discovery object is
generated from the two. The new API is bridge.addDevice({ endpointId, name, categories, ... }) and
device.add(PowerController, options): both throw a DeclarationError that names the endpoint, the interface and
the instance (device/validate.ts), and leave the bridge and the device as they were. AlexaInterface is the same
Capability with the 1.x methods on it; it, ActionMapping and the enums moved to src/compat/, Device to src/device/.

What a 1.x caller can observe:
- every endpoint ends with { type: "AlexaInterface", interface: "Alexa", version: "3" } (alexa-interface.html);
  new Alex2MQTT(..., { alexaInterface: false }) leaves it out
- the fields of a capability object come in the order of Amazon's examples; their content is unchanged
- addCapability() with a name that is not an interface throws (1.5.2 announced it with the version "UNKNOWN")
- ActionMapping takes the payload as an object; a JSON string is parsed (1.5.2 sent the string), any other throws
- what Alexa would reject in a 1.x declaration is not refused: device.check() lists it and the bridge logs each
  line once, as "warning: ..." through the log hook, when it answers a discovery
- a device whose JSON cannot be built is left out of the answer and reported as an error event
- PowerController and EndpointHealth are the descriptors and keep ON/OFF and OK/UNREACHABLE; PowerState is new

Tests: six zoo devices declared the 1.x way give the JSON that Alexa accepted from 1.5.2 on 2026-09-28, plus the
Alexa capability. npm test: 85 pass (was 57) in 10-12 s, also on Node 18.20.8 and 20.20.2.

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

test/fixtures/interfaces.js

@@ -1,11 +1,20 @@
 "use strict";
-// One entry per interface that is described in full: the page its examples were saved from (test/helpers/fixtures.js).
-// test/registry/descriptors.test.js holds every entry against those examples and fails for a descriptor of tier 1 or
-// 2 that has no entry here.
+// One entry per interface that is described in full: the page its examples were saved from (test/helpers/fixtures.js)
+// and declarations that give capability objects of those examples.
+//
+//   namespace   the interface
+//   page        the page of the interface; test/fixtures/alexa-docs/<page>/ has its examples
+//   declared    [{ options, as: [example, n] }]: device.add(descriptor, options) gives the n-th capability object of
+//               the interface in that discovery example (n counts from 0 and defaults to it)
+//
+// test/registry/descriptors.test.js and test/device/discovery.test.js run the entries. The first one fails for a
+// descriptor of tier 1 or 2 that has no entry.
+const reported = { retrievable: true, proactivelyReported: true };
+
 module.exports = [
-  { namespace: "Alexa", page: "alexa-interface" },
-  { namespace: "Alexa.BrightnessController", page: "alexa-brightnesscontroller" },
-  { namespace: "Alexa.EndpointHealth", page: "alexa-endpointhealth" },
-  { namespace: "Alexa.PowerController", page: "alexa-powercontroller" },
-  { namespace: "Alexa.TemperatureSensor", page: "alexa-temperaturesensor" },
+  { namespace: "Alexa", page: "alexa-interface", declared: [{ options: {}, as: ["discovery"] }] },
+  { namespace: "Alexa.BrightnessController", page: "alexa-brightnesscontroller", declared: [{ options: reported, as: ["discovery"] }] },
+  { namespace: "Alexa.EndpointHealth", page: "alexa-endpointhealth", declared: [{ options: reported, as: ["discovery"] }] },
+  { namespace: "Alexa.PowerController", page: "alexa-powercontroller", declared: [{ options: reported, as: ["discovery"] }] },
+  { namespace: "Alexa.TemperatureSensor", page: "alexa-temperaturesensor", declared: [{ options: reported, as: ["discovery"] }] },
 ];