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>

scripts/critical-modules.txt

@@ -8,18 +8,18 @@
 #
 # One module path per line, relative to the repo root. Blank lines and
 # `#` comments are ignored.
-bot_bottle/egress_addon.py
-bot_bottle/egress_addon_core.py
-bot_bottle/dlp_detectors.py
+bot_bottle/gateway/egress/addon.py
+bot_bottle/gateway/egress/addon_core.py
+bot_bottle/gateway/egress/dlp_detectors.py
 bot_bottle/egress.py
 bot_bottle/manifest.py
 bot_bottle/manifest_egress.py
 bot_bottle/manifest_agent.py
 bot_bottle/manifest_schema.py
 bot_bottle/git_gate.py
-bot_bottle/git_gate_render.py
+bot_bottle/gateway/git_gate/render.py
 bot_bottle/git_gate_provision.py
-bot_bottle/git_http_backend.py
+bot_bottle/gateway/git_gate/http_backend.py
 bot_bottle/supervise.py
 bot_bottle/yaml_subset.py
 bot_bottle/bottle_state.py