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/gateway/git_gate/__init__.py

@@ -0,0 +1,7 @@
+"""Gateway-side (data-plane) git-gate service: pure host-side hook rendering
+(PRD 0008) and the smart-HTTP backend that fronts git-gate repos.
+
+The host-side git-gate service (provisioning, preflight) lives in
+`bot_bottle.git_gate`; this is the data-plane counterpart. Import the concrete
+modules directly (`from bot_bottle.gateway.git_gate.render import ...`).
+"""