fish: change cursor options

fish_helix_key_bindings doesn't integrate with Starship, so I need to
ensure the cursor tells me which mode I'm in.

I don't understand *why* it doesn't integrate with Starship. There's
an issue about it on the repo
(sshilovsky/fish-helix#2), and the maintainer
is right - fish-helix DOES set the mode correctly. But, starship doesn't
seem to pick it up? No clue why. If anyone sees this and is able to
figure out why, please let me know somehow! Make an issue or whatever,
I'm happy to personally make the PR.

apps/core/fish/fish-helix.nix

@@ -12,6 +12,7 @@ in
     src = fish-helix;
   };
 
+  # For setting keymap, use `fish_key_reader`
   hm.programs.fish.interactiveShellInit =
   /* fish */
   ''
@@ -20,7 +21,7 @@ in
 
     set fish_cursor_default     block      blink
     set fish_cursor_insert      line       blink
-    set fish_cursor_replace_one underscore blink
-    set fish_cursor_visual      block
+    set fish_cursor_replace_one underscore
+    set fish_cursor_visual      underscore blink
     '';
 }