Pass empty placement explicitly in bar replace

cmd_replace fed $PLACEMENT_FROM_SECTION/$PLACEMENT_FROM_INDEX to jq
without ever calling parse_placement, so they were always empty
strings that implied flag support which does not exist. Pass literal
empties with a comment stating replace resolves by widget id only.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bin/omarchy-bar

@@ -756,11 +756,13 @@ cmd_replace() {
     | .bar.layout[\$source.section][\$source.index].id = \$new
 JQ
 )
+  # resolve_source finds by widget id when no placement is given; replace
+  # takes no placement flags, so pass empty placement explicitly.
   commit "$prog" \
     --arg widgetId "$old" \
     --arg new "$new" \
-    --arg fromSection "$PLACEMENT_FROM_SECTION" \
-    --arg fromIndex "$PLACEMENT_FROM_INDEX"
+    --arg fromSection "" \
+    --arg fromIndex ""
   echo "Replaced $old with $new"
 }