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>

Dockerfile.gateway

@@ -8,8 +8,8 @@
 # this image's mitmproxy / git / gitleaks payload.
 #
 # Collapses the prior per-daemon images (egress, git-gate,
-# supervise) into one. A small stdlib-Python init supervisor at
-# /app/gateway_init.py spawns all daemons, forwards SIGTERM, and
+# supervise) into one. A small stdlib-Python init supervisor
+# (`bot_bottle.gateway.bootstrap`) spawns all daemons, forwards SIGTERM, and
 # propagates per-daemon stdout/stderr to the container log with a
 # `[name]` prefix. See PRD 0024 for the rationale.
 #
@@ -102,7 +102,7 @@ RUN pip install --no-cache-dir /src/
 # WORKDIR here also creates /app so the shim + COPYs below can write into it
 # (nothing created /app before this point).
 WORKDIR /app
-RUN printf 'from bot_bottle.gateway.egress_addon import addons\n' > /app/egress_addon.py
+RUN printf 'from bot_bottle.gateway.egress.addon import addons\n' > /app/egress_addon.py
 COPY bot_bottle/egress_entrypoint.sh /app/egress-entrypoint.sh
 RUN chmod +x /app/egress-entrypoint.sh
 
@@ -123,4 +123,4 @@ EXPOSE 8888 9099 9418 9420 9100
 
 # PID 1 is the supervisor. It owns signal handling and exit-code
 # propagation; no `exec` chain in the entrypoint itself.
-ENTRYPOINT ["python3", "-m", "bot_bottle.gateway.gateway_init"]
+ENTRYPOINT ["python3", "-m", "bot_bottle.gateway.bootstrap"]