email/mu4e: use Emacs mode when viewing mail

Evil masks most of the keybindings that are set by mu4e-view-mode. Since
this is a read-only buffer anyway use Emacs for that mode.

modules/email/mu4e/config.el

@@ -63,6 +63,11 @@
   ;; set mail user agent
   (setq mail-user-agent 'mu4e-user-agent)
 
+  ;; evil masks most mu4e-view-mode key bindings. Switch to Emacs mode for
+  ;; this.
+  (when (featurep! :editor evil)
+    (add-hook! 'mu4e-view-mode-hook #'evil-emacs-state))
+
   ;; Use fancy icons
   (setq mu4e-use-fancy-chars t
         mu4e-headers-draft-mark '("D" . "")