feat(iios): media sharing — presigned storage port + attachments on messages

Media the industry way: the DB stores a reference, bytes live behind a storage port.
- StoragePort + LocalDiskStorage (dev). MediaService presigns short-lived signed
  upload/download URLs (HS256 tokens) pointing at IIOS's own endpoints; the bytes
  never touch the kernel. Prod swaps STORAGE_PORT to S3/Supabase — same as auth.
- MediaController: presign-upload / PUT upload/:token (raw stream) / GET blob/:token /
  presign-download. Uploads are OPA-governed (iios.media.upload: 25 MB cap +
  image/video/audio/pdf/office allowlist); downloads are tenant-fenced by object key.
- send() + MessageDto carry an attachment (contentRef/mimeType/sizeBytes → generic
  MEDIA_REF/VOICE_REF/FILE_REF part; DTO exposes kind image|video|audio|file).

Tests: media.service.spec (6) — round-trip, oversize/type denied, oversized PUT
refused, tampered token rejected, tenant fence. Full suite 192 green. Verified live:
presign→upload→send→history→signed download round-trips the exact bytes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/src/messaging/message.gateway.ts

@@ -91,13 +91,14 @@ export class MessageGateway implements OnGatewayInit, OnGatewayConnection {
   @SubscribeMessage('send_message')
   async sendMessage(
     @ConnectedSocket() client: Socket,
-    @MessageBody() body: { threadId: string; content: string; contentRef?: string; parentInteractionId?: string; mentions?: string[] },
+    @MessageBody()
+    body: { threadId: string; content: string; contentRef?: string; mimeType?: string; sizeBytes?: number; checksumSha256?: string; parentInteractionId?: string; mentions?: string[] },
   ) {
     const { principal } = client.data as SocketState;
     const msg = await this.messages.send(
       body.threadId,
       principal,
-      { content: body.content, contentRef: body.contentRef },
+      { content: body.content, contentRef: body.contentRef, mimeType: body.mimeType, sizeBytes: body.sizeBytes, checksumSha256: body.checksumSha256 },
       randomUUID(),
       undefined,
       body.parentInteractionId,