refactor(gateway): split data-plane files into egress/supervisor/git_gate services

Group the gateway's data-plane modules into three service sub-packages
mirroring the host-side trio (bot_bottle.egress / .supervisor / .git_gate):

  gateway/egress/     addon_core, addon, dlp_config, dlp_detectors
  gateway/supervisor/ server            (was supervise_server)
  gateway/git_gate/   render, http_backend

Prefix-stripped filenames now that the package namespaces them; each
sub-package has a thin docstring __init__ (no eager imports, cheap leaf
loads). The two cross-cutting files stay at the gateway root:
policy_resolver (shared per-client lookup) and gateway_init, renamed to
bootstrap now that gateway/ already namespaces it.

Updated all importers (bot_bottle + tests), the in-VM/container `-m`
launch strings, the Dockerfile.gateway addon shim + ENTRYPOINT, and the
five gateway entries in scripts/critical-modules.txt. Full unit suite
green (2243).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/unit/test_supervise_server.py

@@ -22,8 +22,8 @@ from bot_bottle.orchestrator import supervisor as _sv
 from bot_bottle.orchestrator.store import queue_store as _qs
 from bot_bottle.store import audit_store as _as
 
-from bot_bottle.gateway import supervise_server  # noqa: E402
-from bot_bottle.gateway.supervise_server import (
+from bot_bottle.gateway.supervisor import server as supervise_server  # noqa: E402
+from bot_bottle.gateway.supervisor.server import (
     ERR_INTERNAL,
     ERR_INVALID_PARAMS,
     ERR_INVALID_REQUEST,