feat: web UI protocol 2 client layer, JS and CSS bundles (step 2a)

- data-src/js: ProtoSchema (schema from the sync, short keys and names,
  defaults, cached by hash), ProtoModel (rooms, shades, groups, repeaters,
  header and status from the sync and the events) and ProtoClient (/ws,
  hello, sync with next, op() as a Promise of its reply, events, feeds,
  reconnect). Nothing uses them yet: 2b moves the UI onto them.
- minify.py joins js/*.js and index.js into index.js, and the three CSS
  files into app.css, so a page load opens fewer connections.
- test/js: node --test on the three modules, replaying the recorded
  fixtures; a CI job runs it and the firmware build waits for it.

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

data-src/login.html

@@ -3,9 +3,7 @@
 <head>
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <meta charset="UTF-8">
-    <link rel="stylesheet" href="main.css?v=2.4.0" type="text/css" />
-    <link rel="stylesheet" href="widgets.css?v=2.4.0" type="text/css" />
-    <link rel="stylesheet" href="icons.css?v=2.4.0" type="text/css" />
+    <link rel="stylesheet" href="app.css?v=2.4.0" type="text/css" />
     <link rel="icon" type="image/png" href="favicon.png" />
     <script type="text/javascript" src="index.js?v=2.4.0"></script>
 </head>