feat(prd-0081): reprovision CA, git-gate, and egress tokens on gateway bring-up

On a Firecracker gateway cold boot, reconcile every live agent VM against
the fresh gateway: push the new mitmproxy CA into each agent's trust store,
re-provision git-gate repos/creds from the persisted upstreams snapshot,
and restore egress tokens. Per-bottle failures are logged and skipped so
one unreachable VM does not block the rest.

New modules / changes:
- backend/firecracker/reconcile.py: attach_bottled_agents_to_gateway,
  _push_ca, _reprovision_git_gate, _guest_ip_from_config
- git_gate/provision.py: write upstreams.json after key provisioning so
  the bring-up reconcile can reconstruct the upstream table without the
  manifest
- backend/firecracker/infra.py: call attach_bottled_agents_to_gateway in
  the cold-boot branch of ensure_running()
- backend/base.py: no-op default on BottleBackend
- backend/firecracker/consolidated_launch.py: remove superseded
  _reprovision_running_bottles / _guest_ip_from_config
- orchestrator: OrchestratorCore.update_agent_secret + POST
  /bottles/<id>/secret + client.update_agent_secret (single-secret
  in-place update, the reusable primitive from the 2026-07-26 hotfix)
- tests: 15 new tests in test_firecracker_reconcile.py; updated
  test_firecracker_infra.py cold-boot cases; stale FC reprovision tests
  removed from test_backend_secret_reprovision.py

Closes #516.

bot_bottle/backend/docker/infra.py

@@ -34,7 +34,6 @@ from .orchestrator import (
     ORCHESTRATOR_NETWORK,
 )
 from ... import resources
-from ... import release_manifest
 from ...gateway import (
     GATEWAY_IMAGE,
     GATEWAY_NAME,
@@ -91,14 +90,6 @@ class DockerInfraService(InfraService):
         self._orchestrator_name = orchestrator_name
         self._orchestrator_label = orchestrator_label
         self._gateway_name = gateway_name
-        resolved_orchestrator, orchestrator_local = release_manifest.oci_image(
-            "orchestrator", orchestrator_image)
-        resolved_gateway, gateway_local = release_manifest.oci_image(
-            "gateway", gateway_image)
-        self.orchestrator_image = resolved_orchestrator
-        self.gateway_image = resolved_gateway
-        self._orchestrator_local = orchestrator_local
-        self._gateway_local = gateway_local
 
     def orchestrator(self) -> DockerOrchestrator:
         """The control-plane service. Cheap to reconstruct — `ensure_built`
@@ -113,8 +104,6 @@ class DockerInfraService(InfraService):
             repo_root=self._repo_root,
             host_root=self._host_root,
             root_mount_source=self._root_mount_source,
-            dockerfile=(
-                "Dockerfile.orchestrator" if self._orchestrator_local else None),
         )
 
     def gateway(self) -> DockerGateway:
@@ -130,7 +119,6 @@ class DockerInfraService(InfraService):
             control_network=self.control_network,
             build_context=self._repo_root,
             ca_mount_source=self._gateway_ca_mount_source,
-            dockerfile="Dockerfile.gateway" if self._gateway_local else None,
         )
 
     def ensure_running(
@@ -144,8 +132,8 @@ class DockerInfraService(InfraService):
         gateway = self.gateway()
         # Build both images (cache-aware; a no-op when nothing changed) before
         # bringing either plane up.
-        orchestrator.ensure_available()
-        gateway.ensure_available()
+        orchestrator.ensure_built()
+        gateway.ensure_built()
 
         orchestrator.ensure_running(startup_timeout=startup_timeout)