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/smolmachines/launch.py

@@ -42,19 +42,13 @@ from ..docker.git_gate import (
     GIT_GATE_ENTRYPOINT_IN_CONTAINER,
     GIT_GATE_HOOK_IN_CONTAINER,
 )
-from ..docker.pipelock import pipelock_tls_init
+from ..docker.pipelock import BUNDLE_LOCAL_PIPELOCK_URL, pipelock_tls_init
 from . import sidecar_bundle as _bundle
 from . import smolvm as _smolvm
 from .bottle import SmolmachinesBottle
 from .bottle_plan import SmolmachinesBottlePlan
 
 
-# Pipelock's upstream when egress is in the bundle: localhost on
-# the bundle's own loopback. No docker DNS aliases involved —
-# pipelock + egress share the same container's network namespace.
-_BUNDLE_LOCAL_PIPELOCK_URL = "http://127.0.0.1:8888"
-
-
 @contextmanager
 def launch(
     plan: SmolmachinesBottlePlan,
@@ -95,7 +89,7 @@ def launch(
                 # On smolmachines, egress's upstream is pipelock
                 # on the bundle's localhost — they're in the same
                 # container's network namespace.
-                pipelock_proxy_url=_BUNDLE_LOCAL_PIPELOCK_URL,
+                pipelock_proxy_url=BUNDLE_LOCAL_PIPELOCK_URL,
             )
         plan = dataclasses.replace(
             plan, proxy_plan=proxy_plan, egress_plan=egress_plan,