fix(theme): robbyrussell arrow turns red on command failure (#7440)

Add foreground_templates to the arrow segment so it turns red (#E06C75)
when the previous command exits with a non-zero code, matching the
original oh-my-zsh robbyrussell behavior.

Fixes #7426

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: JanDeDobbeleer

themes/robbyrussell.omp.json

@@ -6,6 +6,7 @@
       "segments": [
         {
           "foreground": "#98C379",
+          "foreground_templates": ["{{ if gt .Code 0 }}#E06C75{{ end }}"],
           "style": "plain",
           "template": "\u279c",
           "type": "text"