feat(bash): prompt for PostgreSQL (#4472)

* feat(install): prompt for SQLite vs PostgreSQL during install

* fix(install): write env file to per-distro path and handle pg-install failure

The env file was hardcoded to /etc/default/x-ui, but RHEL/Fedora units read
/etc/sysconfig/x-ui, Arch reads /etc/conf.d/x-ui, and Alpine OpenRC auto-
sources /etc/conf.d/x-ui. PostgreSQL selection was silently dropped on every
distro except Debian. Also initdb on openSUSE (service wouldn't start) and
prompt the operator on local-install failure instead of silently demoting
to SQLite.

* fix(scripts): make x-ui.sh and update.sh PostgreSQL-aware

update.sh ran setting -show and migrate without sourcing the env file, so
PostgreSQL users had migrations applied to the SQLite default and settings
introspection read the wrong DB. Sourcing the per-distro env file at the
start of update_x-ui exports XUI_DB_TYPE/XUI_DB_DSN to all binary calls.

x-ui.sh now shows the active backend in View Current Settings (password
masked) and removes the env file on uninstall so a later reinstall doesn't
inherit a stale DSN.

update.sh

@@ -105,6 +105,31 @@ gen_random_string() {
         | head -c "$length"
 }
 
+xui_env_file_path() {
+    case "${release}" in
+        ubuntu | debian | armbian)
+            echo "/etc/default/x-ui"
+            ;;
+        arch | manjaro | parch | alpine)
+            echo "/etc/conf.d/x-ui"
+            ;;
+        *)
+            echo "/etc/sysconfig/x-ui"
+            ;;
+    esac
+}
+
+load_xui_env() {
+    local env_file
+    env_file="$(xui_env_file_path)"
+    if [[ -r "$env_file" ]]; then
+        set -a
+        # shellcheck disable=SC1090
+        source "$env_file"
+        set +a
+    fi
+}
+
 install_base() {
     echo -e "${green}Updating and install dependency packages...${plain}"
     case "${release}" in
@@ -775,6 +800,8 @@ config_after_update() {
 update_x-ui() {
     cd ${xui_folder%/x-ui}/
 
+    load_xui_env
+
     if [ -f "${xui_folder}/x-ui" ]; then
         current_xui_version=$(${xui_folder}/x-ui -v)
         echo -e "${green}Current x-ui version: ${current_xui_version}${plain}"