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

bot_bottle/backend/firecracker/bottle_cleanup_plan.py

@@ -10,10 +10,9 @@ from .. import BottleCleanupPlan
 
 @dataclass(frozen=True)
 class FirecrackerBottleCleanupPlan(BottleCleanupPlan):
-    # PIDs of orphaned firecracker VMM processes and the sidecar
-    # containers left behind by previous bottles.
+    # PIDs of orphaned firecracker VMM processes and the per-bottle run
+    # dirs left behind by previous bottles.
     vm_pids: tuple[int, ...] = ()
-    containers: tuple[str, ...] = ()
     run_dirs: tuple[str, ...] = ()
 
     def print(self) -> None:
@@ -22,11 +21,9 @@ class FirecrackerBottleCleanupPlan(BottleCleanupPlan):
             return
         for pid in self.vm_pids:
             info(f"firecracker VM process: pid {pid}")
-        for name in self.containers:
-            info(f"firecracker sidecar container: {name}")
         for path in self.run_dirs:
             info(f"firecracker run dir: {path}")
 
     @property
     def empty(self) -> bool:
-        return not (self.vm_pids or self.containers or self.run_dirs)
+        return not (self.vm_pids or self.run_dirs)