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>

src/db/index.ts

@@ -43,6 +43,7 @@ export {
   createSession,
   getSession,
   findSession,
+  findSessionByAgentGroup,
   getSessionsByAgentGroup,
   getActiveSessions,
   getRunningSessions,
@@ -64,3 +65,18 @@ export {
   updatePendingCredentialMessageId,
   deletePendingCredential,
 } from './credentials.js';
+export {
+  createPendingSwap,
+  getPendingSwap,
+  getInFlightSwapForGroup,
+  getSwapForDevAgent,
+  getAwaitingConfirmationSwaps,
+  getTerminalSwaps,
+  updatePendingSwapStatus,
+  setSwapPreSwapState,
+  startSwapDeadman,
+  extendSwapDeadman,
+  setSwapHandshakeState,
+  resetSwapForRetry,
+  deletePendingSwap,
+} from './pending-swaps.js';