💥 Remove :feature category

:feature was a "catch-all" category. Many of its modules fit better in
other categories, so they've been moved:

- feature/debugger -> tools/debugger
- feature/evil -> editor/evil
- feature/eval -> tools/eval
- feature/lookup -> tools/lookup
- feature/snippets -> editor/snippets
- feature/file-templates -> editor/file-templates
- feature/workspaces -> ui/workspaces

More potential changes in the future:

- A new :term category for terminal emulation modules (eshell, term and
  vterm).
- A new :os category for modules dedicated to os-specific functionality.
  The :tools macos module would fit here, but so would modules for nixos
  and arch.
- A new :services category for web-service integration, like wakatime,
  twitter, elfeed, gist and pastebin services.

modules/app/twitter/autoload.el

@@ -29,7 +29,7 @@ that works with the feature/popup module."
   (interactive "P")
   (condition-case _
       (progn
-        (if (and (not arg) (featurep! :feature workspaces))
+        (if (and (not arg) (featurep! :ui workspaces))
             (+workspace/new +twitter-workspace-name)
           (setq +twitter--old-wconf (current-window-configuration))
           (delete-other-windows)
@@ -52,7 +52,7 @@ that works with the feature/popup module."
   (when (eq major-mode 'twittering-mode)
     (twittering-kill-buffer)
     (cond ((one-window-p) (+twitter/quit-all))
-          ((featurep! :feature workspaces)
+          ((featurep! :ui workspaces)
            (+workspace/close-window-or-workspace))
           ((delete-window)))))
 
@@ -60,7 +60,7 @@ that works with the feature/popup module."
 (defun +twitter/quit-all ()
   "Close all open `twitter-mode' buffers and the associated workspace, if any."
   (interactive)
-  (when (featurep! :feature workspaces)
+  (when (featurep! :ui workspaces)
     (+workspace/delete +twitter-workspace-name))
   (when +twitter--old-wconf
     (set-window-configuration +twitter--old-wconf)