refactor(docker): drop legacy per-sidecar container_name functions

Same line of cleanup as the supervise rename: the per-sidecar
container names (`claude-bottle-pipelock-<slug>`,
`claude-bottle-egress-<slug>`, `claude-bottle-git-gate-<slug>`)
were docker-network aliases pointing at the bundle, kept so legacy
URLs would keep resolving. Replaces them with short hostnames
(`pipelock`, `egress`, `git-gate`) matching the existing
`EGRESS_HOSTNAME` pattern, and inlines the bundle-loopback URL
(`http://127.0.0.1:8888`) for the in-bundle egress→pipelock hop —
matching what smolmachines already does.

Drops the three `*_container_name` functions, `pipelock_proxy_url`,
and `git_gate_host`. Their callers move to the new constants:
- `PIPELOCK_HOSTNAME = "pipelock"` (claude_bottle/pipelock.py)
- `GIT_GATE_HOSTNAME = "git-gate"` (claude_bottle/git_gate.py)
- `BUNDLE_LOCAL_PIPELOCK_URL` (backend/docker/pipelock.py)

The agent's HTTP_PROXY now reads `http://pipelock:8888` (vs the
old `http://claude-bottle-pipelock-<slug>:8888`); the gitconfig
insteadOf rewrites become `git://git-gate/<repo>.git`. The prepare-
time orphan probe is collapsed onto the bundle container name
(`claude-bottle-sidecars-<slug>`) instead of the four legacy
per-sidecar names that no backend creates anymore.

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

claude_bottle/backend/docker/prepare.py

@@ -23,8 +23,6 @@ from ...supervise import Supervise
 from .. import BottleSpec
 from . import util as docker_mod
 from .bottle_plan import DockerBottlePlan
-from .egress import egress_container_name
-from .git_gate import git_gate_container_name
 from .bottle_state import (
     BottleMetadata,
     agent_state_dir,
@@ -39,7 +37,7 @@ from .bottle_state import (
     supervise_state_dir,
     write_metadata,
 )
-from .pipelock import pipelock_container_name
+from .sidecar_bundle import sidecar_bundle_container_name
 
 
 def resolve_plan(
@@ -126,28 +124,18 @@ def resolve_plan(
                 f"clean up old containers with 'docker rm -f <name>'"
             )
 
-    # Probe sidecar container names for orphans from a previous run.
-    # Sidecar names are deterministic from the slug; an orphan would
-    # surface as a docker-create conflict deep inside launch() with no
-    # actionable hint. Fail fast here with a cleanup pointer instead.
-    # Only probe sidecars this launch will actually try to create:
-    # pipelock always; git-gate when bottle.git is non-empty;
-    # egress when bottle.egress.routes is non-empty.
-    sidecar_probes: list[tuple[str, str]] = [
-        ("pipelock", pipelock_container_name(slug)),
-    ]
-    if bottle.git:
-        sidecar_probes.append(("git-gate", git_gate_container_name(slug)))
-    if bottle.egress.routes:
-        sidecar_probes.append(("egress", egress_container_name(slug)))
-    for label, sidecar_name in sidecar_probes:
-        if docker_mod.container_exists(sidecar_name):
-            die(
-                f"{label} sidecar container '{sidecar_name}' already exists. "
-                f"This is an orphan from a previous run; clean it up with "
-                f"'./cli.py cleanup' (or 'docker rm -f {sidecar_name}') and "
-                f"retry."
-            )
+    # Probe the sidecar-bundle container name for an orphan from a
+    # previous run. Otherwise a stale bundle surfaces as a
+    # docker-create conflict deep inside launch() with no actionable
+    # hint; failing fast here points at the cleanup command.
+    bundle_name = sidecar_bundle_container_name(slug)
+    if docker_mod.container_exists(bundle_name):
+        die(
+            f"sidecar bundle container '{bundle_name}' already exists. "
+            f"This is an orphan from a previous run; clean it up with "
+            f"'./cli.py cleanup' (or 'docker rm -f {bundle_name}') and "
+            f"retry."
+        )
 
     # PRD 0018 chunk 2: prepare-time scratch files live under
     # ~/.claude-bottle/state/<slug>/<service>/ so chunk 3's compose