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>

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

@@ -90,8 +90,10 @@ export function initTestSessionDb(): { inbound: Database.Database; outbound: Dat
       content        TEXT NOT NULL
     );
     CREATE TABLE delivered (
-      message_out_id TEXT PRIMARY KEY,
-      delivered_at   TEXT NOT NULL
+      message_out_id      TEXT PRIMARY KEY,
+      platform_message_id TEXT,
+      status              TEXT NOT NULL DEFAULT 'delivered',
+      delivered_at        TEXT NOT NULL
     );
   `);