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_egress_addon_request_flow.py

@@ -194,15 +194,15 @@ def _ensure_shims() -> None:
 
 _ensure_shims()
 
-import bot_bottle.gateway.egress_addon as _ea_mod  # noqa: E402  (after shims)
-from bot_bottle.gateway.egress_addon import EgressAddon  # noqa: E402  (after shims)
-from bot_bottle.gateway.egress_addon import (  # noqa: E402
+import bot_bottle.gateway.egress.addon as _ea_mod  # noqa: E402  (after shims)
+from bot_bottle.gateway.egress.addon import EgressAddon  # noqa: E402  (after shims)
+from bot_bottle.gateway.egress.addon import (  # noqa: E402
     DEFAULT_INBOUND_SCAN_LIMIT_BYTES,
     DEFAULT_TOKEN_ALLOW_TIMEOUT_SECONDS,
     _inbound_scan_limit_from_env,
     _token_allow_timeout_from_env,
 )
-from bot_bottle.gateway.egress_addon_core import (  # noqa: E402
+from bot_bottle.gateway.egress.addon_core import (  # noqa: E402
     Config,
     LOG_BLOCKS,
     LOG_FULL,