refactor(orchestrator): split conflated sidecar image into orchestrator + gateway images

One image — `bot-bottle-sidecars:latest`, built from `Dockerfile.sidecars` —
served two unrelated roles: the egress/git-gate/supervise *data plane* and
the orchestrator *control plane* (which ran the same image with the entrypoint
overridden to `python3 -m bot_bottle.orchestrator`). The control plane is
stdlib-only, so it needed none of the mitmproxy/git/gitleaks payload it was
riding on — while being the most secret-dense process on the host (PRD 0070's
"secret concentration").

Split into two purpose-built images:

- `Dockerfile.gateway` -> `bot-bottle-gateway:latest` — the data plane
  (renamed from Dockerfile.sidecars; identical contents).
- `Dockerfile.orchestrator` -> `bot-bottle-orchestrator:latest` — a lean
  `python:3.12-slim` runtime; the bind-mounted `bot_bottle` package supplies
  the code (so the #381 source-hash recreate semantics are unchanged).

`OrchestratorService` now takes distinct `image` (control plane, default
`ORCHESTRATOR_IMAGE`) and `gateway_image` (data plane, default `GATEWAY_IMAGE`)
instead of feeding one `self.image` to both, and builds the lean image
(build-if-missing) before starting the container. The per-bottle bundle
constants in `backend/docker/sidecar_bundle.py` now alias the gateway
constants so a bundle and the shared gateway can never drift onto different
images. The `bot-bottle-sidecars` *image* name and `Dockerfile.sidecars` are
gone; the per-bottle *container* name prefix (`bot-bottle-sidecars-<slug>`) is
intentionally left for a separate change.

Verified end-to-end: both images build; the lean image runs the control plane;
`ensure_running` brings up the orchestrator on `bot-bottle-orchestrator:latest`
and the gateway on `bot-bottle-gateway:latest` (distinct images) and reports
healthy.

Closes #384.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck

tests/integration/test_orchestrator_docker_gateway_build.py

@@ -21,7 +21,7 @@ IMAGE = "busybox"
 class TestDockerGatewayImageExists(unittest.TestCase):
     def test_image_exists_true_for_present_false_for_absent(self) -> None:
         # Ensure the tiny image is present (build_if_missing is disabled here
-        # so this never triggers a Dockerfile.sidecars build).
+        # so this never triggers a Dockerfile.gateway build).
         subprocess.run(
             ["docker", "pull", IMAGE],
             stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, check=False,

tests/integration/test_sidecar_bundle_image.py

@@ -6,7 +6,7 @@ config (routes.yaml, etc) — that lands in chunk 2 when the
 renderer wires the bundle into compose. What we verify here is
 the chunk-1 contract:
 
-  - Dockerfile.sidecars builds (multi-stage works, base layers
+  - Dockerfile.gateway builds (multi-stage works, base layers
     pull, COPYs resolve).
   - gitleaks, mitmdump are at the documented paths and answer
     `--version`.
@@ -28,8 +28,8 @@ import unittest
 from tests._docker import skip_unless_docker
 
 
-_IMAGE = "bot-bottle-sidecars-test:chunk1"
-_DOCKERFILE = "Dockerfile.sidecars"
+_IMAGE = "bot-bottle-gateway-test:chunk1"
+_DOCKERFILE = "Dockerfile.gateway"
 
 
 @skip_unless_docker()