Allow saving prompts from the Prompt Manager (#12359)

Adds the following features to the prompt manager:

- New prompt – Create a new prompt from the UI. It will only persist if
it is saved.
- Save prompt – Save a prompt by clicking the save button in the UI. A
keybinding will be added for this in the future.
- Reveal prompt - Show the selected prompt on the file system. Only
available for saved prompts.

New prompts that are saved will use the
`{slugified_title}_{ver}_{id}.md` format which all imported prompts will
move to in the near future.

Also orders prompts in alphabetical order by default.

Release Notes:

- N/A

assets/icons/reveal.svg

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+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-folder-search"><circle cx="17" cy="17" r="3"/><path d="M10.7 20H4a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h3.9a2 2 0 0 1 1.69.9l.81 1.2a2 2 0 0 0 1.67.9H20a2 2 0 0 1 2 2v4.1"/><path d="m21 21-1.5-1.5"/></svg>

assets/icons/save.svg

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+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-save"><path d="M15.2 3a2 2 0 0 1 1.4.6l3.8 3.8a2 2 0 0 1 .6 1.4V19a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2z"/><path d="M17 21v-7a1 1 0 0 0-1-1H8a1 1 0 0 0-1 1v7"/><path d="M7 3v4a1 1 0 0 0 1 1h7"/></svg>