Docs: Miren Disks page overstates cloud sync — no mention of universal vs accelerator mode

The disks docs describe cloud sync as a universal property of Miren Disks:

"cloud-synced persistent storage with automatic replication to Miren Cloud" "Your disk data is automatically synced to Miren Cloud" "Data is replicated to Miren Cloud in the background"

This is only true in accelerator mode (requires the lbd kernel module). On a stock VPS — like a Hetzner CX23, which is a very natural place to run Miren — the server silently falls back to universal mode, where disks are local-only with no cloud sync. The user gets no indication this has happened.

We also don't yet have a distribution story for the lbd kernel module (the RFD describes DKMS but it's not shipped), so accelerator mode isn't practically available to users today. This means the cloud sync described in the docs isn't reachable by anyone outside of internal development.

The RFD (0064) is clear about this distinction. The docs flattened it.

Specific issues:

• "cloud-synced" is used as a defining characteristic of Miren Disks with no caveat
• "How Disks Work" step 4 ("Data is replicated to Miren Cloud in the background") is stated unconditionally
• "Automatic backups" is listed as a bullet point benefit — misleading when universal mode has no automatic backup
• The cloud dashboard section describes monitoring "replication progress" that doesn't exist in universal mode
• Universal vs accelerator mode is never mentioned
• There's no guidance on how to tell which mode you're in

Suggested fix: Be honest that cloud sync is not yet available. Reframe Miren Disks around what they do today (managed local persistent storage with on-demand backup via miren backup), and describe cloud sync as a planned capability.