feat: refactor org mode configuration

Defer loading to speed up startup and combine all the configuration of
org mode in the same block.

org-ellipsis is newly added and gives some eye candy when org blocks
are folded.

config.org

@@ -877,26 +877,27 @@ https://github.com/remyferre/comment-dwim-2
     (add-hook 'project-find-functions #'project-projectile)
 )
 #+END_SRC
-
 * Org
 
 ** General config
-*** Super/Sub-scripts
-
-Use ={}= for subscripting:
-
-https://orgmode.org/manual/Subscripts-and-superscripts.html
 
 #+BEGIN_SRC emacs-lisp
-(setq org-use-sub-superscripts '{})
-#+END_SRC
-
-*** Indentation
-
-Preserve indentation in SRC blocks
-
-#+BEGIN_SRC emacs-lisp
-(setq org-src-preserve-indentation t)
+(use-package org
+  :ensure nil
+  :defer t
+  :mode ("\\.org\\'" . org-mode)
+  :config
+  (setq
+   ;; Start collapsed for speed
+   org-startup-folded t
+   ;; Use ={}= for subscripting: https://orgmode.org/manual/Subscripts-and-superscripts.html
+   org-use-sub-superscripts '{}
+   ;; Preserve indentation in SRC blocks
+   org-src-preserve-indentation t
+   )
+  ;; Ellipsis styling
+  (setq org-ellipsis " ▼ ")
+  (set-face-attribute 'org-ellipsis nil :inherit 'default :box nil))
 #+END_SRC
 
 ** Org-todo