refactor(de-sidecar): remove the per-bottle companion-container architecture

The per-agent companion container (the egress/git-gate/supervise data
plane run once per bottle) is the pre-consolidation architecture. Remove
it and disable the backends that still depend on it, per the #385 thread.

- Delete `backend/docker/sidecar_bundle.py`; docker's live path uses the
  consolidated shared gateway, not a per-bottle bundle.
- Disable the firecracker and macos-container backends: their `launch()`
  fails closed (they launched a per-bottle companion; firecracker's
  consolidated relaunch is #354, macos follows). Their `enumerate` return
  empty and `cleanup` drop the companion-container discovery (firecracker
  keeps VMM/run-dir cleanup).
- Fail-close both backends' `egress_apply` reload (it signalled the
  per-bottle container); consolidated egress policy resolves per-request
  against the orchestrator, so gateway-side apply is a follow-up.
- Rename `egress_sidecar_env_entries` → `egress_gateway_env_entries`,
  `SIDECAR_PORTS` → `GATEWAY_PORTS`.
- Move the shared DockerBottlePlan fixture to `tests/unit/_docker_bottle_plan.py`;
  delete tests for the removed launch paths; update cleanup/egress-apply tests.

Docker consolidated launch verified end-to-end (multitenant isolation
integration test passes). macos/firecracker are intentionally disabled.

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

tests/unit/test_macos_container_cleanup.py

@@ -43,27 +43,10 @@ class TestMacosContainerCleanup(unittest.TestCase):
 
 
 class TestMacosContainerEnumerate(unittest.TestCase):
-    def test_enumerate_active_reads_metadata(self):
-        completed = enum_mod.subprocess.CompletedProcess(
-            args=[],
-            returncode=0,
-            stdout="bot-bottle-a\nbot-bottle-sidecars-a\nother\n",
-            stderr="",
-        )
-
-        class _Metadata:
-            agent_name = "impl"
-            started_at = "2026-06-10T00:00:00Z"
-            label = "Implement"
-            color = "blue"
-
-        with patch.object(enum_mod.subprocess, "run", return_value=completed), \
-             patch.object(enum_mod, "read_metadata", return_value=_Metadata()):
-            agents = enum_mod.enumerate_active()
-        self.assertEqual(1, len(agents))
-        self.assertEqual("macos-container", agents[0].backend_name)
-        self.assertEqual("a", agents[0].slug)
-        self.assertEqual("impl", agents[0].agent_name)
+    def test_enumerate_active_is_empty_while_disabled(self):
+        # The macOS backend is disabled during the de-sidecar cleanup
+        # (#385); it launches nothing, so there is nothing to enumerate.
+        self.assertEqual([], enum_mod.enumerate_active())
 
 
 if __name__ == "__main__":