fix(gateway): persist git-gate state across gateway restarts

Per-bottle git-gate state (bare repos under /git/<id>, deploy creds under
/git-gate/creds/<id>) was provisioned once at bottle launch and lived only
in the gateway's ephemeral storage. A gateway rebuild/restart wiped it and
nothing re-provisioned already-running bottles, so their agents 404'd on
fetch/push. Same class of bug as the CA (#510); the orchestrator restores
only egress tokens, not git-gate declarations.

Persist the state on both backends, mirroring the CA-persistence approach:

- firecracker: attach a second persistent data drive (/dev/vdc) to the
  gateway VM and bind-mount its git/ + creds/ subdirs onto /git and
  /git-gate/creds in the gateway guest init, before the data plane starts.
  Generalize the VM config to a stable-ordered data_drives tuple (CA=vdb,
  git=vdc; orchestrator registry stays vdb).
- docker: bind-mount host dirs (host_gateway_git_dir / creds_dir, under the
  never-pruned app-data root) onto /git and /git-gate/creds, with
  BOT_BOTTLE_DOCKER_GIT_MOUNT / _CREDS_MOUNT env overrides so CI isolates
  them to per-run volumes it cleans up.

Teardown already rm -rf's /git/<id> + creds, so the persistent store
self-cleans over the normal lifecycle.

Closes #512

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/unit/test_orchestrator_gateway.py

@@ -161,6 +161,26 @@ class TestDockerGateway(unittest.TestCase):
             "ci-ca-volume:/home/mitmproxy/.mitmproxy", argv
         )
 
+    def test_persists_git_gate_state_across_recreation(self) -> None:
+        # Per-bottle bare repos + deploy creds are bind-mounted from the host so
+        # a gateway restart doesn't drop already-running bottles' git-gate state
+        # (issue #512). Named sources here stand in for CI's per-run volumes.
+        sc = DockerGateway(
+            "bot-bottle-gateway:latest",
+            git_mount_source="ci-git-volume",
+            creds_mount_source="ci-creds-volume",
+        )
+
+        def fake(argv: list[str], **_kw: object) -> Mock:
+            return _proc(stdout="") if argv[:2] == ["docker", "ps"] else _proc()
+
+        with patch(_RUN_DOCKER, side_effect=fake) as run:
+            sc.connect_to_orchestrator(_ORCH_URL, _TOKEN)
+        argv = next(c.args[0] for c in run.call_args_list
+                    if c.args[0][:2] == ["docker", "run"])
+        self.assertIn("ci-git-volume:/git", argv)
+        self.assertIn("ci-creds-volume:/git-gate/creds", argv)
+
     def test_connect_injects_the_pre_minted_gateway_token(self) -> None:
         # The gateway presents the token the orchestrator handed it — it never
         # mints (holds no signing key). The value rides the env (bare `--env