fix: wire v2 setup flow — barrel import, registration, verification

- Import channel barrel from src/index.ts so channel skills that
  uncomment lines in src/channels/index.ts actually execute
- Rewrite setup/register.ts to create v2 entities (agent_groups,
  messaging_groups, messaging_group_agents) in data/v2.db instead
  of v1's store/messages.db
- Fix setup/verify.ts to check v2 central DB for registered groups
- Add prominent "MESSAGE DROPPED" warnings in router when no agent
  groups are wired, with actionable guidance

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

src/index.ts

@@ -19,8 +19,9 @@ import { writeSessionMessage } from './session-manager.js';
 import { wakeContainer } from './container-runner.js';
 import { log } from './log.js';
 
-// Channel imports — each triggers self-registration
-import './channels/discord.js';
+// Channel barrel — each enabled channel self-registers on import.
+// Channel skills uncomment lines in channels/index.ts to enable them.
+import './channels/index.js';
 
 import type { ChannelAdapter, ChannelSetup, ConversationConfig } from './channels/adapter.js';
 import { initChannelAdapters, teardownChannelAdapters, getChannelAdapter } from './channels/channel-registry.js';