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>

bot_bottle/git_gate/service.py

@@ -8,7 +8,7 @@ upstream before fetches. The agent never sees the upstream credential.
 `GitGate` is the host-side service the backend drives at launch: build the plan
 (`prepare`), provision / revoke the per-upstream deploy keys, and preflight the
 upstream host keys. The rendering it emits + the in-gateway hook execution live
-in `bot_bottle.gateway.git_gate_render`.
+in `bot_bottle.gateway.git_gate.render`.
 """
 
 from __future__ import annotations
@@ -16,7 +16,7 @@ from __future__ import annotations
 from pathlib import Path
 
 from ..manifest import Manifest, ManifestBottle
-from ..gateway.git_gate_render import (
+from ..gateway.git_gate.render import (
     GitGateUpstream,
     git_gate_known_hosts_line,
     git_gate_render_access_hook,