fix: isolate chat button from fixed-btn stack to ensure right position

- Move chat-widget outside the floating buttons section in index.html
- Remove fixed-btn class from toggle button (was inheriting left-side
  positioning from the button stack's mobile flex layout)
- Chat widget now renders independently just before body-scripts

templates/partials/widgets/chat-widget.html

@@ -3,7 +3,7 @@
 <!-- AI Chat Widget — CV Assistant Mascot -->
 <button
     id="chat-toggle-btn"
-    class="fixed-btn chat-toggle-btn no-print has-tooltip tooltip-left"
+    class="chat-toggle-btn no-print"
     aria-label="{{if eq .Lang "es"}}Asistente del CV{{else}}CV Assistant{{end}}"
     data-tooltip="{{if eq .Lang "es"}}Asistente del CV{{else}}CV Assistant{{end}}"
     _="on click toggle .chat-open on #chat-panel