feat(v2): builder-agent self-modification WIP + container-config as per-group file

Checkpoints the builder-agent dev-agent/worktree/swap flow (create_dev_agent,
request_swap, classifier, deadman, promote) before pivoting to a unified
draft-activate approach with OS-level RO enforcement. Lifts container_config
out of the agent_groups row into groups/<folder>/container.json so install_packages,
add_mcp_server, and rebuild flows can eventually route through the same draft
path as source edits.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/init-first-agent.ts

@@ -156,7 +156,6 @@ async function main(): Promise<void> {
       name: args.agentName,
       folder,
       agent_provider: null,
-      container_config: null,
       created_at: now,
     });
     ag = getAgentGroupByFolder(folder)!;