webui: pasteLongTextToFileLen is annoying, let's disable it by default

[mashdragon]

I have been using llama.cpp's webui for the past few weeks in browsers where relatively ephemeral local storage means that I keep running into the pasteLongTextToFileLen setting. I've been trying to power through and use the feature, but it has not gone well. I am trying to paste text content into the prompt draft area, and randomly it gets put into a file, which is not what I want.

A few things:

1. The (default) 2,500-character limit after which your pastes get gobbled up is somewhat arbitrary. I simply can't predict what the interface is going to do since there's no way I can quickly estimate the length of my pasted content. A 2,500-character code file looks a lot longer than a 2,500-character essay.
2. You can't send a message after such a paste is made. The UI requires you to type something into the regular prompt space. I've been typing dots because a single space doesn't pass inspection.
3. You can't easily compose messages with this setting.
4. This forces you to draft messages involving large pasted content in an external interface, like Notepad, since there is no way to position your pasted content. It gets caught up into this "file" categorization that is not befitting to all my pastes. And then, of course, this drafted message is over the character limit, and (2) applies, requiring me to include the dot.

How to make it better:

1. Let me be the editor again: let's go back to making pasting work the way you expect by default. webui: Disable pasteLongTextToFileLen by default #14041
2. Keyboard shortcut to enable: For people who do use this feature, enabling it with a keyboard shortcut puts the power back into the user's hands and puts them back into the driver's seat. Now the user knows for sure what pasting into the interface will do instead of getting the lottery based on the length of your content.

Even if other interfaces made this design decision, we can improve upon that in our defaults.