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>

tests/unit/test_provision_git.py

@@ -9,15 +9,15 @@ from tests.fixtures import fixture_minimal, fixture_with_git
 class TestGitGateGitconfigRender(unittest.TestCase):
     def test_empty_entries_renders_nothing(self):
         bottle = fixture_minimal().bottles["dev"]
-        self.assertEqual("", render_git_gate_gitconfig("demo", bottle.git))
+        self.assertEqual("", render_git_gate_gitconfig(bottle.git))
 
     def test_one_block_per_entry(self):
         bottle = fixture_with_git().bottles["dev"]
-        out = render_git_gate_gitconfig("demo", bottle.git)
+        out = render_git_gate_gitconfig(bottle.git)
         # Both entries map to a [url ...] block keyed on the gate's
-        # container hostname (claude-bottle-git-gate-<slug>).
+        # short network alias (`git-gate`) inside the sidecar bundle.
         self.assertIn(
-            '[url "git://claude-bottle-git-gate-demo/claude-bottle.git"]',
+            '[url "git://git-gate/claude-bottle.git"]',
             out,
         )
         self.assertIn(
@@ -25,7 +25,7 @@ class TestGitGateGitconfigRender(unittest.TestCase):
             "ssh://git@gitea.dideric.is:30009/didericis/claude-bottle.git",
             out,
         )
-        self.assertIn('[url "git://claude-bottle-git-gate-demo/foo.git"]', out)
+        self.assertIn('[url "git://git-gate/foo.git"]', out)
         self.assertIn(
             "\tinsteadOf = ssh://git@github.com/didericis/foo.git",
             out,
@@ -37,7 +37,7 @@ class TestGitGateGitconfigRender(unittest.TestCase):
         # gate push and leave fetch on the original URL — exactly the
         # v1 design we've moved past.
         bottle = fixture_with_git().bottles["dev"]
-        out = render_git_gate_gitconfig("demo", bottle.git)
+        out = render_git_gate_gitconfig(bottle.git)
         self.assertIn("\tinsteadOf", out)
         self.assertNotIn("pushInsteadOf", out)