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/git_gate.py

@@ -1,9 +1,8 @@
-"""Docker-side git-gate helpers: in-container paths the renderer's
-bind-mounts target, port pin, and container naming. The
-prepare-time entrypoint/hook render lives on the platform-neutral
-`GitGate` ABC — backends instantiate it directly. The git-gate
-daemon's container lifecycle is owned by the sidecar bundle
-(PRD 0024)."""
+"""Docker-side git-gate constants: in-container paths the renderer's
+bind-mounts target + the listening port. The prepare-time entrypoint
+/ hook render lives on the platform-neutral `GitGate` ABC — backends
+instantiate it directly. The git-gate daemon's container lifecycle
+is owned by the sidecar bundle (PRD 0024)."""
 
 from __future__ import annotations
 
@@ -15,18 +14,3 @@ GIT_GATE_CREDS_DIR_IN_CONTAINER = "/git-gate/creds"
 
 # git daemon's default listening port.
 GIT_GATE_PORT = 9418
-
-
-def git_gate_container_name(slug: str) -> str:
-    """The legacy per-sidecar container name. Kept as a function so
-    the renderer can register it as a docker-network alias on the
-    bundle — any code still dialing `claude-bottle-git-gate-<slug>`
-    resolves to the bundle's IP."""
-    return f"claude-bottle-git-gate-{slug}"
-
-
-def git_gate_host(slug: str) -> str:
-    """The hostname the agent's git client connects to. Resolves via
-    the bundle's network alias to the bundle container, where the
-    git-gate daemon listens on GIT_GATE_PORT."""
-    return git_gate_container_name(slug)