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- backend/firecracker/consolidated_launch.py: remove superseded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/firecracker/infra_vm.py

@@ -43,7 +43,6 @@ from pathlib import Path
 from typing import Generator
 
 from ... import resources
-from ... import release_manifest
 from ...log import die, info
 from ..docker import util as docker_mod
 from . import firecracker_vm, infra_artifact, netpool, util
@@ -109,18 +108,6 @@ def _role_version(role: str) -> str:
     return infra_artifact.infra_artifact_version(role_init(role), role)
 
 
-def _role_release(role: str) -> tuple[str, str | None]:
-    manifest = release_manifest.packaged_manifest()
-    if manifest is None or release_manifest.local_build_requested():
-        return _role_version(role), None
-    artifact = (
-        manifest.firecracker_orchestrator
-        if role == "orchestrator"
-        else manifest.firecracker_gateway
-    )
-    return artifact.version, artifact.sha256
-
-
 def ensure_built() -> None:
     """Ensure both infra rootfs artifacts are available before boot.
 
@@ -130,16 +117,11 @@ def ensure_built() -> None:
     `BOT_BOTTLE_INFRA_BUILD=local` instead builds the images from source with
     host Docker (the orchestrator-fc image is `FROM` the orchestrator image, so
     it must exist first) — for iterating on the Dockerfiles."""
-    if release_manifest.local_build_requested():
+    if infra_artifact.local_build_requested():
         build_infra_images_with_docker()
         return
     for role in infra_artifact.ROLES:
-        version, expected = _role_release(role)
-        infra_artifact.ensure_artifact_gz(
-            version, role=role, expected_sha256=expected)
-
-
-ensure_available = ensure_built
+        infra_artifact.ensure_artifact_gz(_role_version(role), role=role)
 
 
 def build_infra_images_with_docker() -> None:
@@ -232,9 +214,7 @@ def boot_vm(
     else:
         # Prebuilt artifact already carries the role's build slack; expand it to
         # a fresh writable rootfs for this boot.
-        version, expected = _role_release(role)
-        infra_artifact.materialize_ext4(
-            version, rootfs, role=role, expected_sha256=expected)
+        infra_artifact.materialize_ext4(_role_version(role), rootfs, role=role)
     private_key, pubkey = _stable_keypair()
 
     info(f"booting {role} VM on {slot.iface} (guest {slot.guest_ip})")
@@ -284,8 +264,7 @@ def _version_file() -> Path:
 def expected_version() -> str:
     """The combined marker for the running pair: both per-plane artifact
     versions, so a change to either rootfs dislodges the adopted pair."""
-    return " ".join(
-        f"{role}={_role_release(role)[0]}" for role in infra_artifact.ROLES)
+    return " ".join(f"{role}={_role_version(role)}" for role in infra_artifact.ROLES)
 
 
 def adoptable(key: Path, url: str, want: str) -> bool: