[Rework] WebUI: migrate BS5 off jQuery bridge

[Rework] WebUI: migrate BS5 off jQuery bridge

Replace the Bootstrap 5 jQuery bridge (.modal/.popover/.trigger
"click.bs.dropdown") with the vanilla constructor API
(bootstrap.{Modal,Popover,Dropdown}.getOrCreateInstance) in
rspamd.js, config.js and libft.js, capturing the bootstrap module
where needed.

Prerequisite for removing jQuery: the bridge only activates when
jQuery is loaded, while the vanilla API works regardless. With jQuery
still present the existing $(el).on("*.bs.*") subscriptions keep
firing, so those stay jQuery for now and move to addEventListener
together with the rest of the jQuery removal. The main.js shim
deps:["jquery"] becomes redundant and is dropped in the final stage.