feat(kanban): smooth drop slot instead of a flickering line; fix reload after reordering

The column works out the slot from the pointer (cards no longer handle drag enter/leave, which
flickered on their child elements); a gap of the card's height opens there with framer-motion,
the dragged card leaves its old place and lights up where it lands.

The realtime handler reloaded with the loadData of its first render ("Alle Aufgaben"), so a
selected list showed other lists' tasks after TASK_REORDERED; it now calls the current one.
v0.38.1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "mindsift-frontend",
   "private": true,
-  "version": "0.38.0",
+  "version": "0.38.1",
   "license": "Unlicense",
   "type": "module",
   "scripts": {