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_egress.py

@@ -16,7 +16,7 @@ from bot_bottle.egress import (
     egress_render_routes,
     egress_resolve_token_values,
     egress_routes_for_bottle,
-    egress_sidecar_env_entries,
+    egress_gateway_env_entries,
     egress_token_env_map,
 )
 from bot_bottle.errors import MissingEnvVarError
@@ -603,7 +603,7 @@ class TestEgressEnvEntries(unittest.TestCase):
                 "CANON_ALPHA_SECRET=fake-canary-value",
                 "BOT_BOTTLE_SENSITIVE_PREFIXES=CANON_ALPHA_SECRET",
             ),
-            egress_sidecar_env_entries(plan),
+            egress_gateway_env_entries(plan),
         )
 
     def test_agent_entries_include_only_canary_bait(self):
@@ -630,7 +630,7 @@ class TestEgressEnvEntries(unittest.TestCase):
             canary="fake-canary-value",
         )
 
-        self.assertEqual((), egress_sidecar_env_entries(plan))
+        self.assertEqual((), egress_gateway_env_entries(plan))
         self.assertEqual((), egress_agent_env_entries(plan))