Can add multiple same name devices despite what the "Add Device" dialog infers

### Current Behavior

The "Add Device" dialog states **"Provide a unique, identifiable name for your device."** but does not inhibit the user adding "same named" devices.

https://github.com/flowforge/flowforge/assets/44235289/946fb999-9622-4992-bccf-b8cd61c4cfbc

### Expected Behavior

There are several ways we _could_ handle this:

1. Add a DB index/unique constraint.
1. Though this might impact existing users
2. Inhibit future new devices having the same name (block at API level)
3. Change the dialog text to **"It is recommended you provide a unique name for your device."**
1. Effectively permitting the use of same name devices but discouraging it.

### Steps To Reproduce

Add device with name of existing device

### Environment

- FlowForge version: 1.11

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate

Start with the Add Device dialog and trace the device API and data model. The issue presents three possible resolutions—database uniqueness, API validation, or revised dialog text—so confirm the intended policy with maintainers before changing anything. Done means duplicate-name behavior and the dialog wording consistently match that decision, with the reproduce case covered.

Written by the indexing model from the issue text.