feat: agent-to-agent communication, dynamic agent creation, self-modification tools

Agent-to-agent: host routes messages with channel_type='agent' to target
agent's inbound.db, enriches with sender info, wakes target container.
Bidirectional routing works via inherited routing context.

Dynamic agents: create_agent MCP tool + system action handler creates
agent groups, folders, and optional CLAUDE.md on the fly.

Self-modification: install_packages (apt/npm, requires admin approval),
add_mcp_server (no approval), request_rebuild (builds per-agent-group
Docker image with approved packages). Approval flow reuses interactive
card infrastructure with pending_approvals table.

Also includes fixes from prior session: attachment download, reply context
extraction, message editing (platform message ID tracking), delivery retry
limits, and card update on button click.

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

src/db/migrations/index.ts

@@ -3,6 +3,7 @@ import type Database from 'better-sqlite3';
 import { log } from '../../log.js';
 import { migration001 } from './001-initial.js';
 import { migration002 } from './002-chat-sdk-state.js';
+import { migration003 } from './003-pending-approvals.js';
 
 export interface Migration {
   version: number;
@@ -10,7 +11,7 @@ export interface Migration {
   up: (db: Database.Database) => void;
 }
 
-const migrations: Migration[] = [migration001, migration002];
+const migrations: Migration[] = [migration001, migration002, migration003];
 
 export function runMigrations(db: Database.Database): void {
   db.exec(`