refactor(sidecars): drop vestigial start/stop methods (PRD 0024 chunk 3)

Compose-up has owned per-container lifecycle since PRD 0018 ch3;
the .start() / .stop() methods on DockerPipelockProxy /
DockerEgress / DockerGitGate / DockerSupervise (and their
abstractmethod declarations in the four base ABCs) were already
documented as vestigial. With the bundle path in flight
(PRD 0024 ch2), they are truly dead — collapse to nothing.

Changes:
- Removed start/stop methods from the four DockerSidecar
  classes. Plan dataclasses, image/path constants,
  container-name helpers, and the .prepare() methods all stay
  (the renderer + apply path still need them).
- Removed the matching @abstractmethod declarations in the
  base ABCs so concrete subclasses don't have to stub them.
- launch.launch() and prepare.resolve_plan() no longer take
  proxy/git_gate/egress/supervise instance parameters. backend.py
  loses the four instance attributes it threaded through.
  prepare.resolve_plan() instantiates the four classes itself
  to call their .prepare() methods.
- Deleted four integration tests that only exercised the
  removed lifecycle: test_pipelock_sidecar_smoke,
  test_supervise_sidecar, test_git_gate_sidecar,
  test_git_gate_mirror.
- Dropped the .stop-idempotency case in test_orphan_cleanup;
  the network-cleanup cases stay (those test real production
  code).
- Marked test_pipelock_apply @skip pending chunk 4 — its
  bringup helper used .start; chunk 4 rewrites it with direct
  `docker run`.

Dockerfile deletion deferred to chunk 5 (when the bundle flag
default flips) — the legacy compose path still needs
Dockerfile.{egress,git-gate,supervise} until then.

Net: 708 lines removed, 80 added.

533 unit tests + 27 integration tests passing (5 skipped: the
chunk-4-pending case + existing GITEA_ACTIONS guards).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/integration/test_orphan_cleanup.py

@@ -1,8 +1,13 @@
-"""Integration: the cleanup primitives the start-flow trap depends on
-are idempotent. The original orphan-network bug was a trap-ordering
-issue; the fix moved the install earlier. The trap is only safe if
-network_remove and PipelockProxy.stop are no-ops against missing
-resources."""
+"""Integration: the network-cleanup primitives the start-flow trap
+depends on are idempotent. The original orphan-network bug was a
+trap-ordering issue; the fix moved the install earlier. The trap
+is only safe if network_remove is a no-op against missing
+resources.
+
+The PipelockProxy.stop idempotency case that used to live here was
+removed in PRD 0024 chunk 3 when the per-container .stop method
+went away — sidecar teardown is now compose's responsibility, and
+`compose down` already no-ops on missing containers."""
 
 import os
 import subprocess
@@ -13,10 +18,6 @@ from claude_bottle.backend.docker.network import (
     network_create_internal,
     network_remove,
 )
-from claude_bottle.backend.docker.pipelock import (
-    DockerPipelockProxy,
-    pipelock_container_name,
-)
 from tests._docker import skip_unless_docker
 
 
@@ -71,10 +72,6 @@ class TestOrphanCleanup(unittest.TestCase):
         self.assertTrue(network_remove(self.internal_name))
         self.assertTrue(network_remove(self.egress_name))
 
-    def test_pipelock_stop_missing_sidecar(self):
-        # Should not raise.
-        DockerPipelockProxy().stop(pipelock_container_name(f"missing-{self.slug}"))
-
 
 if __name__ == "__main__":
     unittest.main()