feat: group multi-browser output by source

- Add browser source grouping metadata to SDK-created tabs, groups,
  list results, and aggregate count results.
- Render grouped local/remote browser tables consistently for clients,
  tabs, groups, windows, sessions, and remote status output.
- Document remote control, auth, HTTP gateway usage, and the refreshed
  project structure in the README.
- Add coverage for grouped output and BrowserCounts browser_groups.
- Bump the Python package, extension manifest, and lockfile to 0.15.6.
- Add a just publish helper for building and publishing release artifacts.

justfile

@@ -74,6 +74,18 @@ version-check:
      ext=$(grep -m1 '"version"' extension/manifest.json | cut -d'"' -f4); \
      if [ "$py" = "$ext" ]; then echo "ok: $py"; else echo "MISMATCH pyproject=$py manifest=$ext"; exit 1; fi
 
+# Build into /tmp/dist-browser-cli and publish using credentials from .env
+publish:
+    #!/usr/bin/env bash
+    set -euo pipefail
+    set -a
+    [ ! -f .env ] || source .env
+    set +a
+    rm -rf /tmp/dist-browser-cli
+    mkdir -p /tmp/dist-browser-cli
+    uv build --out-dir /tmp/dist-browser-cli
+    uv publish /tmp/dist-browser-cli/*
+
 # ── Demos ──────────────────────────────────────────────────────────────
 
 # Run the Python SDK demo