refactor(gateway): move the data-plane daemons into a bot_bottle.gateway package

Separate the gateway (data plane) from the orchestrator (control plane) at the
module level. The gateway runtime files move out of the package root — and the
backend-neutral Gateway lifecycle ABC + GATEWAY_* constants move out of
orchestrator/ — into a new bot_bottle/gateway/ package:

  gateway/__init__.py      (was orchestrator/gateway.py: Gateway ABC + consts
                            + rotate_gateway_ca)
  gateway/gateway_init.py  (the PID-1 daemon supervisor)
  gateway/egress_addon.py, egress_addon_core.py, egress_dlp_config.py,
          dlp_detectors.py            (the egress mitmproxy daemon)
  gateway/git_http_backend.py         (the git-http daemon)
  gateway/git_gate_render.py          (the git-gate pre-receive rendering)
  gateway/supervise_server.py         (the supervise MCP daemon)
  gateway/policy_resolver.py          (the data-plane control-plane RPC client)

orchestrator/ now holds only control-plane files. The shared plan/types/auth
layer (egress.py=EgressPlan, git_gate.py=GitGatePlan, supervise.py,
supervise_types.py, control_auth.py) and the launch-time git-gate provisioning
helpers stay at root, so orchestrator/ and backend/ still own them.

Because these daemons are invoked as `python3 -m bot_bottle.<name>`, loaded flat
by mitmproxy, and referenced in Dockerfile.gateway, the move updates more than
Python imports: the `-m` invocations (firecracker/macOS infra scripts), the
Dockerfile.gateway addon shim + ENTRYPOINT, gateway_init's _DAEMONS module
paths, and the git-gate CGI heredocs all now point at bot_bottle.gateway.*.

No behavior change; full unit suite green (2251).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Dockerfile.gateway

@@ -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.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_init"]
+ENTRYPOINT ["python3", "-m", "bot_bottle.gateway.gateway_init"]