Companion Buttons 1.0.0: any Companion button from any page, live on a ProdDash tile

A ProdDash module for status buttons and what's happening: pick buttons from
any Companion page in the tile's own picker; each is shown exactly as
Companion draws it and redraws live. One tile can hold one button or many.

- One read-only connection to Companion's tRPC websocket (pages.watch and
  preview.graphics.controlId), shared by every dashboard; identical redraws
  are not re-sent.
- A tile follows its button by id, and by page/row/column when the id is
  gone (a re-imported page), saving back what it resolved to.
- One SSE stream per tile, within ProdDash's 32-streams-per-page limit.
- Red dot and a faded "Companion offline" view when Companion is down;
  recovers by itself.
- Tests against a mock Companion: node test/companion.test.js

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

module.json

@@ -0,0 +1,33 @@
+{
+  "id": "companion-buttons",
+  "name": "Companion Buttons",
+  "version": "1.0.0",
+  "proddash": ">=1.10.0",
+  "description": "Any Companion button from any page, live as Companion draws it — for status and what's happening",
+  "permissions": [
+    {
+      "kind": "local-network",
+      "reason": "Reading button pictures from Companion on this network"
+    }
+  ],
+  "client": "client.js",
+  "server": "server.js",
+  "style": "style.css",
+  "minSize": { "w": 1, "h": 1 },
+  "defaultSize": { "w": 3, "h": 3 },
+  "configSchema": {
+    "companion": {
+      "type": "endpoint",
+      "label": "Companion",
+      "default": { "host": "", "port": 8000 },
+      "help": "The machine running Bitfocus Companion and its web interface port (8000 unless changed in Companion's settings). 127.0.0.1 when Companion runs on this machine. Companion 4 or newer."
+    }
+  },
+  "instanceSchema": {
+    "captions": {
+      "type": "switch",
+      "label": "Captions",
+      "default": false
+    }
+  }
+}