feat: Integrate consult with xref and enhance denote backlink commands

- Configure consult-xref for xref-show-definitions and xref-show-xrefs
- Add custom denote backlink commands with consult preview support
- Replace denote-backlinks keybindings with new consult-enabled versions
- Fix hardcoded org path to use org-directory variable

lisp/init-completion.el

@@ -35,9 +35,14 @@
    (*is-linux*
     (setq consult-locate-args "plocate --basename --ignore-case")))
 
+  ;; help
   (define-key consult-narrow-map (vconcat consult-narrow-key "?") #'consult-narrow-help)
   (setq consult-narrow-key "<")
 
+  ;; xref
+  (setq xref-show-definitions-function #'consult-xref)
+  (setq xref-show-xrefs-function #'consult-xref)
+
   ;; set some buffer filter
   (setq consult-buffer-filter
         (cl-union consult-buffer-filter