v2 phase 1: foundation — types, DB layer, logging

Add the v2 data layer: typed interfaces, central DB with migration
runner, per-entity CRUD, and agent-runner session DB operations.

- src/log.ts: concise message-first logging API
- src/types-v2.ts: AgentGroup, MessagingGroup, Session, MessageIn/Out
- src/db/: connection (WAL), migration runner, 001-initial schema,
  CRUD for agent_groups, messaging_groups, sessions, pending_questions
- container/agent-runner/src/db/: session DB connection, messages_in
  reads + status transitions, messages_out writes
- 31 new tests, all 277 tests pass

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

container/agent-runner/src/db/index.ts

@@ -0,0 +1,5 @@
+export { getSessionDb, initTestSessionDb, closeSessionDb } from './connection.js';
+export { getPendingMessages, markProcessing, markCompleted, markFailed, getMessageIn, findQuestionResponse } from './messages-in.js';
+export type { MessageInRow } from './messages-in.js';
+export { writeMessageOut, getUndeliveredMessages, markDelivered } from './messages-out.js';
+export type { MessageOutRow, WriteMessageOut } from './messages-out.js';