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>

packages/db/migrations/meta/_journal.json

@@ -64,6 +64,13 @@
       "when": 1775477883426,
       "tag": "0008_add-state-and-memory",
       "breakpoints": true
+    },
+    {
+      "idx": 9,
+      "version": "7",
+      "when": 1775480008546,
+      "tag": "0009_add-file-tables",
+      "breakpoints": true
     }
   ]
 }