feat(git): use remote default branch to guess main branch (#13212)

Co-authored-by: Carlo Sala <carlosalag@protonmail.com>

plugins/git/git.plugin.zsh

@@ -31,10 +31,12 @@ function git_develop_branch() {
   return 1
 }
 
-# Check if main exists and use instead of master
+# Get the default branch name from common branch names or fallback to remote HEAD
 function git_main_branch() {
   command git rev-parse --git-dir &>/dev/null || return
-  local ref
+  
+  local remote ref
+  
   for ref in refs/{heads,remotes/{origin,upstream}}/{main,trunk,mainline,default,stable,master}; do
     if command git show-ref -q --verify $ref; then
       echo ${ref:t}
@@ -42,6 +44,14 @@ function git_main_branch() {
     fi
   done
   
+  # Fallback: try to get the default branch from remote HEAD symbolic refs
+  for remote in origin upstream; do
+    ref=$(command git rev-parse --abbrev-ref $remote/HEAD 2>/dev/null)
+    if [[ $ref == $remote/* ]]; then
+      echo ${ref#"$remote/"}; return 0
+    fi
+  done
+
   # If no main branch was found, fall back to master but return error
   echo master
   return 1