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/backend/firecracker/infra_vm.py

@@ -542,7 +542,7 @@ BOT_BOTTLE_ROOT=/var/lib/bot-bottle BOT_BOTTLE_CONTROL_PLANE_TOKEN="$CP_KEY" pyt
 BOT_BOTTLE_GATEWAY_DAEMONS=egress,git-http,supervise \\
 BOT_BOTTLE_ORCHESTRATOR_URL=http://127.0.0.1:{CONTROL_PLANE_PORT} \\
 BOT_BOTTLE_CONTROL_AUTH_JWT="$GW_JWT" \\
-    python3 -m bot_bottle.gateway.gateway_init &
+    python3 -m bot_bottle.gateway.bootstrap &
 
 # Reap as PID 1; children are backgrounded, so `wait` blocks.
 while : ; do wait ; done