Add /clear command

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

web/src/whatsnew.ts

@@ -3,6 +3,10 @@
  * under "unreleased"; scripts/release.sh renames the key to the release version.
  */
 export const WHATS_NEW: Record<string, { en: string[]; de: string[] }> = {
+  unreleased: {
+    en: ["/clear: the model forgets the conversation so far, the chat stays visible"],
+    de: ["/clear: das Modell vergisst das bisherige Gespräch, der Chat bleibt sichtbar"],
+  },
   "202611-00029": {
     en: [
       "Statistics: foldable sections, years of history with a year filter, export as XLSX/CSV",