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>

minify.py

@@ -52,6 +52,16 @@ MINIFY_AND_GZIP = {".html", ".htm", ".css", ".js", ".json", ".svg", ".xml"}
 # Extensions that optipng can optimise
 PNG_EXTENSIONS = {".png"}
 
+# Files joined into one, in this order, before they are minified: a page load
+# then opens fewer connections, each of which costs the device heap
+# (docs/adr/0005-one-websocket-protocol.md).  The protocol 2 client in js/
+# comes before index.js, which uses it.  A source listed here isn't copied on
+# its own.
+BUNDLES = {
+    "index.js": ["js/schema.js", "js/model.js", "js/client.js", "index.js"],
+    "app.css": ["main.css", "widgets.css", "icons.css"],
+}
+
 # Everything else is copied verbatim
 # ──────────────────────────────────────────────
 
@@ -252,6 +262,33 @@ def minify_all():
     total_final = 0
     file_count = 0
 
+    def report(rel_path, stats):
+        nonlocal total_original, total_final, file_count
+        pct = (1 - stats["final"] / stats["original"]) * 100 if stats["original"] > 0 else 0
+        print(
+            f"  {rel_path:<40s} "
+            f"{stats['original']:>8,d} → {stats['final']:>8,d} B "
+            f"({pct:+.0f}%)  [{stats['action']}]"
+        )
+        total_original += stats["original"]
+        total_final += stats["final"]
+        file_count += 1
+
+    bundled = set()
+    work_dir = os.path.join(dst_dir, ".bundles")
+    os.makedirs(work_dir, exist_ok=True)
+    for name, parts in BUNDLES.items():
+        joined = os.path.join(work_dir, name)
+        with open(joined, "w", encoding="utf-8") as out:
+            for part in parts:
+                with open(os.path.join(src_dir, part), "r", encoding="utf-8") as f:
+                    out.write(f.read())
+                # A file without a final newline would run into the next.
+                out.write("\n")
+                bundled.add(os.path.normpath(part))
+        report(f"{name} ({len(parts)} files)", process_file(joined, os.path.join(dst_dir, name)))
+    shutil.rmtree(work_dir)
+
     for root, dirs, files in os.walk(src_dir):
         for fname in sorted(files):
             # Skip hidden files and editor temp files
@@ -260,20 +297,11 @@ def minify_all():
 
             src_path = os.path.join(root, fname)
             rel_path = os.path.relpath(src_path, src_dir)
+            if os.path.normpath(rel_path) in bundled:
+                continue
             dst_path = os.path.join(dst_dir, rel_path)
 
-            stats = process_file(src_path, dst_path)
-
-            pct = (1 - stats["final"] / stats["original"]) * 100 if stats["original"] > 0 else 0
-            print(
-                f"  {rel_path:<40s} "
-                f"{stats['original']:>8,d} → {stats['final']:>8,d} B "
-                f"({pct:+.0f}%)  [{stats['action']}]"
-            )
-
-            total_original += stats["original"]
-            total_final += stats["final"]
-            file_count += 1
+            report(rel_path, process_file(src_path, dst_path))
 
     print(f"[minify] {file_count} files processed")
     print(