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/src/env.ts

@@ -20,6 +20,10 @@ const envSchema = z.object({
   MAX_CONNECTIONS_PER_MESH: z.coerce.number().int().positive().default(100),
   MAX_MESSAGE_BYTES: z.coerce.number().int().positive().default(65_536),
   HOOK_RATE_LIMIT_PER_MIN: z.coerce.number().int().positive().default(30),
+  MINIO_ENDPOINT: z.string().default("minio:9000"),
+  MINIO_ACCESS_KEY: z.string().default("claudemesh"),
+  MINIO_SECRET_KEY: z.string().default("changeme"),
+  MINIO_USE_SSL: z.coerce.boolean().default(false),
   NODE_ENV: z
     .enum(["development", "production", "test"])
     .default("development"),