registry: Speaker, StepSpeaker, EqualizerController, PlaybackController, PlaybackStateReporter, InputController, ChannelController

Seven descriptors written from their pages replace seven stubs. All are version 3; 1.5.2 announced Speaker,
StepSpeaker, EqualizerController and PlaybackStateReporter as version 1, and all but ChannelController without
a property. StepSpeaker has no properties object in discovery and PlaybackController one without fields, next
to supportedOperations; a directive for an operation the device did not list is answered with
INVALID_DIRECTIVE. The equalizer declares bands, modes or both under "configurations", a TV its inputs from
the 61 names of the page.

Not described: the lineup of ChannelController, whose discovery example the page folds away. The discovery
examples of InputController spell one key "friendNames"; the fixtures have friendlyNames, as its table does.
62 examples of the six pages are saved as fixtures. 241 tests pass, 215 before.

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

test/fixtures/alexa-docs/alexa-equalizercontroller/discovery.json

@@ -0,0 +1,94 @@
+{
+  "event": {
+    "header": {
+      "namespace": "Alexa.Discovery",
+      "name": "Discover.Response",
+      "payloadVersion": "3",
+      "messageId": "Unique identifier, preferably a version 4 UUID"
+    },
+    "payload": {
+      "endpoints": [
+        {
+          "endpointId": "Unique ID of the endpoint",
+          "manufacturerName": "Manufacturer of the endpoint",
+          "description": "Smart Television by Television Maker",
+          "friendlyName": "Living Room TV",
+          "displayCategories": [
+            "TV"
+          ],
+          "cookie": {},
+          "capabilities": [
+            {
+              "type": "AlexaInterface",
+              "interface": "Alexa.EqualizerController",
+              "version": "3",
+              "properties": {
+                "supported": [
+                  {
+                    "name": "bands"
+                  },
+                  {
+                    "name": "mode"
+                  }
+                ],
+                "retrievable": true,
+                "proactivelyReported": true
+              },
+              "configurations": {
+                "bands": {
+                  "supported": [
+                    {
+                      "name": "BASS"
+                    },
+                    {
+                      "name": "MIDRANGE"
+                    },
+                    {
+                      "name": "TREBLE"
+                    }
+                  ],
+                  "range": {
+                    "minimum": -6,
+                    "maximum": 6
+                  }
+                },
+                "modes": {
+                  "supported": [
+                    {
+                      "name": "MOVIE"
+                    },
+                    {
+                      "name": "MUSIC"
+                    },
+                    {
+                      "name": "SPORT"
+                    }
+                  ]
+                }
+              }
+            },
+            {
+              "type": "AlexaInterface",
+              "interface": "Alexa.PowerController",
+              "version": "3",
+              "properties": {
+                "supported": [
+                  {
+                    "name": "powerState"
+                  }
+                ],
+                "retrievable": true,
+                "proactivelyReported": true
+              }
+            },
+            {
+              "type": "AlexaInterface",
+              "interface": "Alexa",
+              "version": "3"
+            }
+          ]
+        }
+      ]
+    }
+  }
+}