feat(ssh-gate)!: remove ssh-gate sidecar and provisioner (PRD 0009)

Delete claude_bottle/ssh_gate.py, the DockerSSHGate sidecar,
and the provision_ssh provisioner (~/.ssh/config + ssh-agent
wiring). Unwire the gate from the abstract BottleBackend
(provision orchestration drops the ssh step,
_validate_ssh_entries goes away) and from the Docker backend
(prepare/launch lose the `gate` kwarg, bottle_plan drops the
gate_plan field, dry-run JSON drops the ssh_hosts / ssh_gate
keys, y/N preflight drops the ssh-hosts block). cli/info now
prints declared git remotes instead of ssh hosts. pipelock's
docstring picks up the git-gate framing now that there's no
PRD-0007 boundary to call out.

BREAKING (dry-run JSON): the `ssh_hosts` and `ssh_gate` keys
are gone from `start --dry-run --format=json`. Consumers should
read `git_remotes` / `git_gate` instead.

claude_bottle/backend/docker/launch.py

@@ -25,7 +25,6 @@ from .bottle_plan import DockerBottlePlan
 from .git_gate import DockerGitGate
 from .pipelock import DockerPipelockProxy, pipelock_proxy_url, pipelock_tls_init
 from .provision.ca import AGENT_CA_BUNDLE, AGENT_CA_PATH
-from .ssh_gate import DockerSSHGate
 
 
 # Where the repo root lives, for `docker build` context. Computed once.
@@ -37,7 +36,6 @@ def launch(
     plan: DockerBottlePlan,
     *,
     proxy: DockerPipelockProxy,
-    gate: DockerSSHGate,
     git_gate: DockerGitGate,
     provision: Callable[[DockerBottlePlan, str], str | None],
 ) -> Generator[DockerBottle, None, None]:
@@ -89,21 +87,6 @@ def launch(
         pipelock_name = proxy.start(plan.proxy_plan)
         stack.callback(proxy.stop, pipelock_name)
 
-        # SSH egress gate (PRD 0007). One sidecar per agent, only
-        # brought up when the bottle has ssh entries. Lives on the
-        # same internal + egress networks pipelock straddles; the
-        # agent dials it by container name (DNS works on --internal,
-        # confirmed by the PRD 0007 spike).
-        if plan.gate_plan.upstreams:
-            gate_plan = dataclasses.replace(
-                plan.gate_plan,
-                internal_network=internal_network,
-                egress_network=egress_network,
-            )
-            plan = dataclasses.replace(plan, gate_plan=gate_plan)
-            gate_name = gate.start(plan.gate_plan)
-            stack.callback(gate.stop, gate_name)
-
         # Git gate (PRD 0008). One sidecar per agent, only brought up
         # when the bottle has git entries. Same internal + egress
         # network attachment as the other sidecars; agent dials it as