refactor: ui.js, chat.js, history.js in 13 modulare Dateien aufteilen

Die monolithische ui.js (1534 Zeilen) zusammen mit chat.js (612) und
history.js (626) in fokussierte Module aufgeteilt:

Neue Dateien aus ui.js:
- ui-helpers.js (126) - DOM-Utilities, $, esc, truncate, scrollDown, Toast
- markdown.js (143) - renderMarkdown, wrapKreaGalleries, LaTeX/Code-Schutz
- cards.js (90) - buildSessionCard, buildAgentCard
- msg-actions.js (208) - Delete, Mark, Share, Reply-Button, Timestamp
- tool-ui.js (332) - Tool-Boxes, Diffs, Todo-Liste, Visibility
- modals.js (190) - System-Prompt, Command-Output, Krea-Image Modals
- stream-ui.js (124) - Stream-Bubble, Review-Streaming
- bubbles.js (312) - User/Assistant/Error/Warning/Choice/Review Bubbles

Neue Dateien aus chat.js:
- reply.js (54) - Reply/Quote-Handling mit pendingReply State
- files.js (110) - File-Upload, Workspace-Refs mit pendingFiles/Refs State

Neue Datei aus history.js:
- archive.js (173) - Archiv-Loading mit loadedArchiveCount State

Verbleibend:
- chat.js (448) - Stream-Events, sendMessage, handleChoiceClick, Plan-Mode
- history.js (464) - History laden, Polling, Message-Rendering

Kein Code verändert, nur verschoben. Alle 94 Funktionen verifiziert.
Globale Variablen in die Module verschoben, wo sie primär genutzt werden.

wwwroot/js/reply.js

@@ -0,0 +1,54 @@
+// ── Reply / Quote ──
+
+let pendingReply = null; // { index, role, text } - Zitierte Nachricht
+
+function _formatReplyTimestamp(ts) {
+  if (!ts) return 'Jetzt';
+  try {
+    const d = new Date(ts);
+    const now = new Date();
+    const hh = d.getHours().toString().padStart(2, '0');
+    const mm = d.getMinutes().toString().padStart(2, '0');
+    // Gleiches Datum → nur Uhrzeit, sonst Datum + Uhrzeit
+    if (d.toDateString() === now.toDateString()) {
+      return hh + ':' + mm;
+    }
+    const dd = d.getDate().toString().padStart(2, '0');
+    const mo = (d.getMonth() + 1).toString().padStart(2, '0');
+    return dd + '.' + mo + '. ' + hh + ':' + mm;
+  } catch { return 'Jetzt'; }
+}
+
+function setReply(reply) {
+  pendingReply = reply;
+  renderReplyPreview();
+  document.getElementById('input')?.focus();
+}
+
+function clearReply() {
+  pendingReply = null;
+  renderReplyPreview();
+}
+
+function renderReplyPreview() {
+  const container = $('#replyPreview');
+  if (!container) return;
+
+  if (!pendingReply) {
+    container.innerHTML = '';
+    container.hidden = true;
+    return;
+  }
+
+  const roleLabel = pendingReply.role === 'user' ? 'User' : 'Assistant';
+  const timeLabel = _formatReplyTimestamp(pendingReply.timestamp);
+  const preview = truncate(pendingReply.text, 150);
+
+  container.innerHTML = `<div class="reply-preview-item">
+    <span class="reply-icon"><i class="fa fa-reply"></i></span>
+    <span class="reply-meta">${esc(timeLabel)}, ${esc(roleLabel)}</span>
+    <span class="reply-text">${esc(preview)}</span>
+    <button class="file-remove" onclick="clearReply()"><i class="fa fa-times"></i></button>
+  </div>`;
+  container.hidden = false;
+}