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/unit/test_orchestrator_gateway.py

@@ -24,7 +24,7 @@ def _proc(returncode: int = 0, stdout: str = "", stderr: str = "") -> Mock:
 
 class TestDockerGateway(unittest.TestCase):
     def setUp(self) -> None:
-        self.sc = DockerGateway("bot-bottle-sidecars:latest")
+        self.sc = DockerGateway("bot-bottle-gateway:latest")
 
     def test_default_name(self) -> None:
         self.assertEqual(GATEWAY_NAME, self.sc.name)
@@ -86,7 +86,7 @@ class TestDockerGateway(unittest.TestCase):
         runs = [c for c in calls if c[:2] == ["docker", "run"]]
         self.assertEqual(1, len(runs))
         self.assertIn(self.sc.name, runs[0])
-        self.assertIn("bot-bottle-sidecars:latest", runs[0])
+        self.assertIn("bot-bottle-gateway:latest", runs[0])
         # Runs on the shared gateway network so agents can reach it by IP.
         self.assertEqual(self.sc.network, runs[0][runs[0].index("--network") + 1])
         # Persists its CA on a named volume so agents keep trusting it.
@@ -183,7 +183,7 @@ class TestDockerGatewayBuild(unittest.TestCase):
         builds = [c for c in calls if c[:2] == ["docker", "build"]]
         self.assertEqual(1, len(builds))
         self.assertIn(self.sc.image_ref, builds[0])
-        self.assertTrue(any(a.endswith("Dockerfile.sidecars") for a in builds[0]))
+        self.assertTrue(any(a.endswith("Dockerfile.gateway") for a in builds[0]))
         self.assertNotIn("--no-cache", builds[0])
 
     def test_ensure_built_no_cache_env_forces_full_rebuild(self) -> None: