feat: Reply/Zitat-Feature für Chat-Nachrichten

- Reply-Button (Hover) auf jeder User/Assistant-Nachricht
- Reply-Preview-Leiste über dem Input-Feld (mit Timestamp, Rolle, Text-Preview)
- Beim Senden: Zitat als Kontext-Block vorangestellt (> [Zitat: HH:MM, Role]:)
- User-Nachrichten parsen Zitat-Blöcke als visuelle Quote-Elemente (blaue Borderlinie)
- Timestamp-basierte Referenzierung (HH:MM oder DD.MM. HH:MM)
- clearReply() bei Chat-Clear, Navigation und Destroy

wwwroot/css/chat.css

@@ -262,6 +262,97 @@
   margin-inline: auto;
 }
 
+/* Reply Button */
+
+.msg {
+  position: relative;
+}
+
+.msg-reply-btn {
+  position: absolute;
+  top: var(--badge-spacing);
+  right: var(--badge-spacing);
+  opacity: 0;
+  transition: opacity .15s;
+  padding: .15em .35em;
+  font-size: var(--font-size);
+  background: var(--f2-bg);
+  border: var(--border-width) solid var(--f2-border);
+  border-radius: var(--border-radius);
+}
+
+.msg:hover .msg-reply-btn {
+  opacity: var(--semi-transparent);
+}
+
+.msg-reply-btn:hover {
+  opacity: 1 !important;
+}
+
+/* Reply Quote in User Bubble */
+
+.reply-quote {
+  border-left: 3px solid var(--primary);
+  padding: var(--badge-padding);
+  padding-left: var(--box-spacing);
+  margin-bottom: var(--box-spacing);
+  opacity: var(--semi-transparent);
+  white-space: normal;
+}
+
+.reply-quote-meta {
+  font-size: var(--font-size);
+  margin-bottom: .2em;
+  color: var(--primary);
+}
+
+.reply-quote-text {
+  font-size: var(--font-size);
+}
+
+/* Reply Preview */
+
+.reply-preview {
+  padding: var(--box-padding);
+  padding-bottom: 0;
+}
+
+.reply-preview:not([hidden]) {
+  display: flex;
+}
+
+.reply-preview-item {
+  display: flex;
+  align-items: center;
+  padding: var(--badge-padding);
+  gap: var(--badge-spacing);
+  background: var(--f2-bg);
+  border: var(--border-width) solid var(--f2-border);
+  border-radius: var(--border-radius);
+  border-left: 3px solid var(--primary);
+  overflow: hidden;
+  flex: 1;
+}
+
+.reply-icon {
+  flex-shrink: 0;
+  color: var(--primary);
+}
+
+.reply-meta {
+  flex-shrink: 0;
+  font-weight: bold;
+  font-size: var(--font-size);
+}
+
+.reply-text {
+  flex: 1;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  opacity: var(--semi-transparent);
+}
+
 /* Workspace Refs */
 
 .ref-preview {