fix: Use git to figure out git repo. (#351)

I have a `.git` directory in my `$HOME` for some git hooks I have but it
isn't a git repo and confuses me when I open a new terminal and forget
I'm in my home but I get the 'There were more than 150 changed files.'
I've included how it should look with the `/tmp` directory. See
screenshot.

<img width="843" height="175" alt="ss 2025-08-04 at 12 33 52 PM"
src="https://github.com/user-attachments/assets/d2eaf852-c298-40d8-bace-b67a54df2a5e"
/>

This removes the `find_in_cwd_or_parent` shell method in favor of just
using a `git` command to determine. Seems simpler and more stable since
it uses built-in git behaviour instead of rolling our own method.

Author: ghthor

lib/git/helpers.sh

@@ -1,14 +1,7 @@
-function find_in_cwd_or_parent() {
-  local slashes=${PWD//[^\/]/}; local directory=$PWD;
-  for (( n=${#slashes}; n>0; --n )); do
-    test -e "$directory/$1" && echo "$directory/$1" && return 0
-    directory="$directory/.."
-  done
-  return 1
-}
-
 function fail_if_not_git_repo() {
-  if ! find_in_cwd_or_parent ".git" > /dev/null; then
+  local gcmd=${_git_cmd:-git}
+
+  if ! "${gcmd}" rev-parse --show-toplevel &> /dev/null; then
     echo -e "\033[31mNot a git repository (or any of the parent directories)\033[0m"
     return 1
   fi