feat(secrets): encrypt egress tokens at rest with per-bottle ENV_VAR_SECRET

Implements the interim secret-provider design (PRD prd-new-secret-provider):
each agent receives a random ENV_VAR_SECRET injected into its container env
at launch. The host uses this key to encrypt each egress auth token value
(HMAC-SHA256 CTR mode, stdlib-only) and store it in a new
bottled_agent_secrets table (one row per env var, key column plaintext for
auditing). The key never touches the DB.

On infra container restart the in-memory token map is lost. launch_consolidated
now calls _reprovision_running_bottles after ensure_running: for each
registered bottle still alive on the gateway network it execs
`printenv ENV_VAR_SECRET` into the agent container and posts the result to the
new POST /bottles/<id>/reprovision_gateway control-plane endpoint, which
decrypts the stored rows and restores _tokens — no manual intervention needed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bot_bottle/backend/docker/consolidated_compose.py

@@ -17,6 +17,7 @@ from __future__ import annotations
 from typing import Any
 
 from ...egress import egress_agent_env_entries
+from ...orchestrator.secret_store import ENV_VAR_SECRET_NAME
 from ..util import AGENT_CA_BUNDLE, AGENT_CA_PATH
 from .bottle_plan import DockerBottlePlan
 from .egress import EGRESS_PORT
@@ -58,6 +59,10 @@ def consolidated_agent_compose(
     # the secret value never lands on argv or in the compose file.
     for name in sorted(plan.forwarded_env.keys()):
         env.append(name)
+    # ENV_VAR_SECRET: bare name so the value comes from the compose subprocess
+    # env (set in launch.py) and is never written to the compose file on disk.
+    if getattr(plan, "env_var_secret", ""):
+        env.append(ENV_VAR_SECRET_NAME)
     env.extend(egress_agent_env_entries(plan.egress_plan))
 
     service: dict[str, Any] = {