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>

test/e2e/test_survival.py

@@ -54,7 +54,7 @@ def test_one_client_too_many_is_closed(connect, schema):
 
 def test_page_load(host, token, connect, watch_heap):
     """The static files in parallel, as a browser fetches them, then the socket."""
-    files = ["/", "/main.css", "/widgets.css", "/icons.css", "/index.js", "/icon.png"]
+    files = ["/", "/app.css", "/index.js", "/icon.png"]
     errors = []
 
     def get(path):