Suppress output in non-interactive shells

Add is_interactive_shell() helper and gate all user-visible
echo/debug output behind it so that non-interactive invocations
(scripts, cron, ssh commands) stay silent. Move functions.sh
source earlier in bashrc so helpers are available sooner.

functions.sh

@@ -5,6 +5,10 @@ if [ -z "$time_ms" ]; then
     readonly time_ms='date +%s%3N'
 fi
 
+function is_interactive_shell() {
+    [[ $- == *i* ]]
+}
+
 function is_fast_init() {
     (( $LWS_FAST ))
 }
@@ -14,7 +18,7 @@ function is_slow_init() {
 }
 
 function xlog() {
-  if true_false "$LWS_DEBUG"; then
+  if is_interactive_shell && true_false "$LWS_DEBUG"; then
     echo "$@"
   fi
 }
@@ -100,11 +104,11 @@ function source_directory() {
   xlog "LOAD DIR $mask"
   for file in $mask; do
     if [[ -e "$file" ]]; then
-      if (( $LWS_DEBUG )); then
+      if is_interactive_shell && (( $LWS_DEBUG )); then
         start=$($time_ms)
         source "$file"
         stop=$($time_ms)
-        echo "LOAD FILE $file $((stop - start)) ms"
+        xlog "LOAD FILE $file $((stop - start)) ms"
       else
         source "$file"
       fi