feat: v0.4.0 — File sharing + multi-target messages

Files: MinIO-backed file sharing built into the broker.
share_file for persistent mesh files, send_message(file:) for
ephemeral attachments. Presigned URLs for download, access
tracking per peer.

Broker infra: MinIO in docker-compose, internal network.
HTTP POST /upload endpoint. WS handlers for get_file,
list_files, file_status, delete_file.

Multi-target: send_message(to:) accepts string or array.
Targets deduplicated before delivery.

Targeted views: MCP instructions teach Claude to send
tailored messages per audience instead of generic broadcasts.

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

apps/broker/package.json

@@ -19,6 +19,7 @@
     "@turbostarter/shared": "workspace:*",
     "drizzle-orm": "0.44.7",
     "libsodium-wrappers": "0.7.15",
+    "minio": "8.0.7",
     "ws": "8.20.0",
     "zod": "catalog:"
   },