fix: improve filtering ux

[davidsanchez222]

Changes made:

• added a visible filter input line at the top of the left pane so you can see what you’re typing.
• made filtering explicit so you can only filter once you type /. i added this because there are some letters like [a, n, d, t, g, q] that wouldn't start searching and would instead give you a popup. this fails when my layout starts with any of these letters. For example, I couldn't search for a layout named new_layout
• added a hint type to filter so you can see where you are going to type only after entering filter mode
• added navigation key binds (ctrl-n/ctrl-p, ctrl-j/ctrl-k, tab/shift-tab) so you can select a layout without exiting filter mode. it also wraps around once you reach the end
• finally, i updated the help text and added unit tests to cover this new logic and the removal of quick search.

If you wanted to keep quick search, you could make the [a, n, d, t, g, q] settings uppercase i.e. [A, N, D, T, G, Q] but again you run the risk of someone having a layout with any of those uppercase letters. having an explicit key to start searching is a better design imo

[Franvy]

Thanks for the PR, @davidsanchez222! 🙌 Got it — I'll take a look as soon as I have some time. Appreciate your patience!