On Save error, custom prompt modal should return to custom prompt modal

[i13-ctflora]

• Disable all other plugins besides Copilot (required)
• Screenshot of note + Copilot chat pane + dev console added (required)

Copilot version: 2.7.9

Describe how to reproduce
When saving a custom prompt, if there are illegal characters in the prompt name (such as ":") then an error is logged and you're kicked back to the main Obsidian screen. This means you lose the custom prompt you've just entered.

Expected behavior
After the error, you should instead return to the modal, where your prompt name is highlighted with error styling. Additionally, the prompt you've entered should still be there.

Ideally, the error styling should happen immediately in the modal on entering the forbidden characters, or at least a note should be present indicating that these particular characters are not allowed.

Screenshots

Additional context
Not a huge deal, but pretty frustrating when you've entered a fairly long prompt without realizing that ":" were not acceptable in the name, and then having to re-do the prompt a second time.
Also - the Obsidian notification that flashes up briefly indicates that the problem is another custom prompt of the same name, not the character problem which is only visible in the browser console.