move theme toggle to own Vue app for better tab order

Relocate the light/dark toggle button out of #app1 and into a new
#app3 mount just before the back-to-top element so keyboard focus
reaches it near the end of the page instead of right after the main
nav. Replace the library logo's reactive :src binding with a plain
src plus data-light-src/data-dark-src so app1 no longer needs any
theme state; app3 now owns toggleTheme, overlay updates, logo swap,
and the OS preference listener.

groups/home/bootstrap5/home1.html

@@ -80,7 +80,9 @@
               id="library-logo"
               class="image-fail"
               alt="Kibbee Library logo"
-              :src="isDark ? 'https://d2jv02qf7xgjwx.cloudfront.net/accounts/16298/images/Kibbee_library_logo_inverted2.jpg' : 'https://libapps.s3.amazonaws.com/accounts/16298/images/xsmall-2.jpg'"
+              src="https://libapps.s3.amazonaws.com/accounts/16298/images/xsmall-2.jpg"
+              data-light-src="https://libapps.s3.amazonaws.com/accounts/16298/images/xsmall-2.jpg"
+              data-dark-src="https://d2jv02qf7xgjwx.cloudfront.net/accounts/16298/images/Kibbee_library_logo_inverted2.jpg"
             />
             {{content_box_33471502}}
           </div>
@@ -94,14 +96,6 @@
           <!-- end of col-xs-12 -->
         </div>
         <!--end of row-->
-        <button
-          id="theme-toggle"
-          @click="toggleTheme"
-          :aria-label="isDark ? 'Switch to light mode' : 'Switch to dark mode'"
-          type="button"
-        >
-          <i :class="isDark ? 'fas fa-sun' : 'fas fa-moon'" aria-hidden="true"></i>
-        </button>
       </div>
       <!--end of Vue app1-->
     </div>
@@ -369,6 +363,16 @@
     <i class="fas fa-sync fa-spin" aria-hidden="true"></i> Loading...
     <button class="btn btn-secondary btn-sm popclose" type="button">Close</button>
   </div>
+  <div id="app3">
+    <button
+      id="theme-toggle"
+      @click="toggleTheme"
+      :aria-label="isDark ? 'Switch to light mode' : 'Switch to dark mode'"
+      type="button"
+    >
+      <i :class="isDark ? 'fas fa-sun' : 'fas fa-moon'" aria-hidden="true"></i>
+    </button>
+  </div>
   <div id="s-lib-scroll-top" title="Back to Top">
     <span class="fa-stack fa-lg" aria-hidden="true">
       <i class="far fa-square fa-stack-2x"></i>