feat: named destinations + permission enforcement + fire-and-forget self-mod

Replaces implicit routing context (NANOCLAW_PLATFORM_ID env vars) with
per-agent named destination maps. Agents reference channels and peer
agents by local names; the host re-validates every outbound route against
a new agent_destinations table that is both the routing map and the ACL.

Model changes:
- New migration 004 adds agent_destinations (agent_group_id, local_name,
  target_type, target_id). Backfills from existing messaging_group_agents.
- Host writes /workspace/.nanoclaw-destinations.json before every container
  wake so admin changes take effect on next start.
- Container loads map at startup, appends system-prompt addendum listing
  available destinations and the <message to="name">…</message> syntax.
- Agent main output is parsed for <message to="..."> blocks; each block
  becomes a messages_out row with routing resolved via the local map.
  Untagged text and <internal>…</internal> are scratchpad (logged only).
- send_message MCP tool now takes `to` (destination name) instead of raw
  routing fields. send_to_agent deleted (redundant — agents are just
  destinations). send_file/edit_message/add_reaction route via map too.
- Inbound formatter adds from="name" attribute via reverse-lookup so the
  agent sees a consistent namespace in both directions.

Permission enforcement:
- Host checks hasDestination() before every channel delivery AND every
  agent-to-agent route. Unauthorized messages dropped and logged.
- routeAgentMessage simplified: ~15 lines, no JSON parse, content copied
  verbatim (target formatter resolves the sender via its own local map).
- create_agent is admin-only, checked at both the container (tool not
  registered for non-admins) and the host (re-check on receive). Inserts
  bidirectional destination rows so parent↔child comms work immediately.
  Includes path-traversal guard on folder name.

Self-modification cleanup:
- add_mcp_server now requires admin approval (previously had none).
- install_packages validates package names on BOTH sides (container tool
  + host receiver) with strict regex. Max 20 packages per request.
- All three self-mod tools are fire-and-forget: write request, return
  immediately with "submitted" message. Admin approval triggers a chat
  notification to the requesting agent — no tool-call polling, no 5-min
  holds. On rebuild/mcp_server approval, the container is killed so the
  next wake picks up new config/image.
- Approval delivery extracted into requestApproval() helper (the one
  place where three call sites were literally identical).

Also folded in the phase-1 dynamic import cleanup (create_agent no longer
does `await import('./db/agent-groups.js')`) and removes NANOCLAW_PLATFORM_ID
/ CHANNEL_TYPE / THREAD_ID env-var routing entirely.

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

container/agent-runner/src/formatter.ts

@@ -1,3 +1,4 @@
+import { findByRouting } from './destinations.js';
 import type { MessageInRow } from './db/messages-in.js';
 
 /**
@@ -123,7 +124,19 @@ function formatSingleChat(msg: MessageInRow): string {
   const idAttr = msg.seq != null ? ` id="${msg.seq}"` : '';
   const replyPrefix = formatReplyContext(content.replyTo);
   const attachmentsSuffix = formatAttachments(content.attachments);
-  return `<message${idAttr} sender="${escapeXml(sender)}" time="${time}">${replyPrefix}${escapeXml(text)}${attachmentsSuffix}</message>`;
+
+  // Look up the destination name for the origin (reverse map lookup).
+  // If not found, fall back to a raw channel:platform_id marker so nothing
+  // gets silently dropped — this should only happen if the destination was
+  // removed between when the message was received and when it's being processed.
+  const fromDest = findByRouting(msg.channel_type, msg.platform_id);
+  const fromAttr = fromDest
+    ? ` from="${escapeXml(fromDest.name)}"`
+    : msg.channel_type || msg.platform_id
+      ? ` from="unknown:${escapeXml(msg.channel_type || '')}:${escapeXml(msg.platform_id || '')}"`
+      : '';
+
+  return `<message${idAttr}${fromAttr} sender="${escapeXml(sender)}" time="${time}">${replyPrefix}${escapeXml(text)}${attachmentsSuffix}</message>`;
 }
 
 function formatTaskMessage(msg: MessageInRow): string {