refactor(box): launch box runtime via the lbp CLI subcommand

Mirror the plugin runtime: box is now started through the same CLI entry
point (langbot_plugin.cli) instead of the box module directly.

- docker-compose.yaml: langbot_box command runs `langbot_plugin.cli ... box`
  (WebSocket is the default transport, no flag needed — matches `rt`).
- box/connector.py: both subprocess launch sites (_start_local_stdio and
  the Windows _start_subprocess_then_ws path) invoke
  `langbot_plugin.cli.__init__ box`, using `-s` for the stdio transport.
- docs/review: update stale `-m langbot_plugin.box[.server]` references.

Pairs with the SDK change that removes box's direct-launch entry points
(python -m langbot_plugin.box / .box.server) and the legacy --mode flag.

docker/docker-compose.yaml

@@ -43,7 +43,12 @@ services:
       # The Box runtime does NOT read box.local.* from config.yaml or env; it
       # receives its configuration from LangBot via the INIT RPC action.
       # Do not add LANGBOT_BOX_* / BOX__* here — they would be silently ignored.
-    command: ["uv", "run", "--no-sync", "-m", "langbot_plugin.box", "--mode", "ws"]
+    # Launched through the same CLI entry point as the plugin runtime
+    # (`langbot_plugin.cli.__init__ <subcommand>`). WebSocket is the default
+    # control transport — mirrors `rt`, which also runs with no flag. Pass
+    # `-s` / `--stdio-control` only for the stdio mode LangBot uses outside
+    # containers.
+    command: ["uv", "run", "--no-sync", "-m", "langbot_plugin.cli.__init__", "box"]
     networks:
       - langbot_network