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>

dist/esm/device/Capability.js

@@ -0,0 +1,63 @@
+import { s } from "../registry/schema.js";
+/** The same as a schema. The friendly names are checked with the instance, by the rules of the interface. */
+export const commonOptions = s.object({
+    instance: s.optional(s.string()),
+    friendlyNames: s.optional(s.array(s.unknown())),
+    retrievable: s.optional(s.boolean()),
+    proactivelyReported: s.optional(s.boolean()),
+    nonControllable: s.optional(s.boolean()),
+});
+/** One interface as an endpoint declares it: the descriptor, and what the declaration says about this endpoint. */
+export class Capability {
+    constructor(descriptor, declared) {
+        this.descriptor = descriptor;
+        /** The endpoint the capability is declared on; the device sets it. */
+        this.endpointId = "";
+        /** What the bridge logs about the declaration, once, when it answers a discovery. */
+        this.notes = [];
+        this.instance = declared.instance ?? "";
+        this.friendlyNames = declared.friendlyNames ?? [];
+        this.retrievable = declared.retrievable ?? true;
+        this.proactivelyReported = declared.proactivelyReported ?? false;
+        this.nonControllable = declared.nonControllable;
+        this.options = declared.options;
+    }
+    get namespace() {
+        return this.descriptor.namespace;
+    }
+    /** Mappings of "open", "close", "raise", "lower" and of states, when the declaration has any. */
+    get semantics() {
+        const { semantics } = this.options;
+        const mapped = (semantics?.actionMappings?.length ?? 0) + (semantics?.stateMappings?.length ?? 0);
+        return mapped > 0 ? semantics : undefined;
+    }
+    /** The capability object for discovery, its fields in the order of the example on alexa-discovery-objects.html. */
+    toJSON() {
+        const { descriptor, semantics } = this;
+        const extras = descriptor.discovery ? descriptor.discovery(this) : {};
+        const json = {
+            type: "AlexaInterface",
+            interface: descriptor.namespace,
+            ...(this.instance ? { instance: this.instance } : {}),
+            version: descriptor.version,
+        };
+        if (extras.properties !== false) {
+            json.properties = {
+                supported: Object.keys(descriptor.properties).map((name) => ({ name })),
+                proactivelyReported: this.proactivelyReported,
+                retrievable: this.retrievable,
+            };
+            if (this.nonControllable !== undefined)
+                json.properties.nonControllable = this.nonControllable;
+        }
+        if (this.friendlyNames.length > 0)
+            json.capabilityResources = { friendlyNames: this.friendlyNames };
+        if (extras.configuration)
+            json.configuration = extras.configuration;
+        if (extras.configurations)
+            json.configurations = extras.configurations;
+        if (semantics)
+            json.semantics = semantics;
+        return { ...json, ...extras.topLevel };
+    }
+}