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/test-v2-host.ts

@@ -38,7 +38,6 @@ createAgentGroup({
   name: 'E2E Test Agent',
   folder: 'test-agent-e2e',
   agent_provider: 'claude',
-  container_config: null,
   created_at: new Date().toISOString(),
 });