feat: Split _path_add into _path_append and _path_prepend

_path_add only ever appended to PATH, which didn't fit profile.d/krew
and profile.d/anyenv (they prepend, to take priority). Rename it to
_path_append for clarity and add _path_prepend alongside it, so both
orderings get the same dedup guard when needed — krew and anyenv
aren't converted yet, kept as plain PATH concatenation until then.

_helpers.bash

@@ -25,12 +25,18 @@ function _source_dir_files() {
 }
 
 # Source : https://superuser.com/questions/39751/add-directory-to-path-if-its-not-already-there
-_path_add() {
+_path_append() {
 	if [ -d "$1" ] && [[ ":${PATH}:" != *":$1:"* ]]; then
 		PATH="${PATH:+"${PATH}:"}$1"
 	fi
 }
 
+_path_prepend() {
+	if [ -d "$1" ] && [[ ":${PATH}:" != *":$1:"* ]]; then
+		PATH="$1${PATH:+":${PATH}"}"
+	fi
+}
+
 _prompt_command_add() {
 	if [ -n "$1" ] && [[ ":${PROMPT_COMMAND}:" != *":$1:"* ]]; then
 		PROMPT_COMMAND="${PROMPT_COMMAND:+"${PROMPT_COMMAND};"}$1"