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/validate.d.ts

@@ -0,0 +1,20 @@
+import type { AnyDescriptor, Declared, EndpointView } from "../registry/types.js";
+/** An endpoint as discovery sends it, without its capabilities. */
+export interface EndpointFields {
+    endpointId: string;
+    friendlyName: string;
+    description: string;
+    manufacturerName: string;
+    displayCategories: readonly string[];
+    additionalAttributes: Readonly<Record<string, string>>;
+    cookie?: Readonly<Record<string, string>>;
+}
+/** Throws the first rule of the Endpoint object that the fields break. */
+export declare function checkEndpoint(endpoint: EndpointFields): void;
+/** alexa-discovery.html, "Interface limits". count includes the capabilities the library adds. */
+export declare function checkCapabilityCount(endpointId: string, count: number): void;
+/**
+ * Throws the first rule that a capability breaks on its endpoint. endpoint.capabilities are the ones declared
+ * before it. A stub is checked for being declared twice and for nothing else: the library does not know its rules.
+ */
+export declare function checkCapability(capability: Declared<unknown>, descriptor: AnyDescriptor, endpoint: EndpointView): void;