Fix interaction-mode toggle default icon and tooltip

The toggle button was defaulting to 'Pan Mode' with a plus-icon path,
but the actual default interaction mode is 'select' (the cursor/arrow).
Update the tooltip to 'Select Mode' and replace the SVG path with an
arrow/cursor shape so the icon matches the active mode at startup.

reader.html

@@ -368,11 +368,11 @@
     <button
       id="interaction-mode-toggle"
       aria-label="Toggle pan/select mode"
-      title="Pan Mode"
+      title="Select Mode"
       style="display: none"
     >
       <svg class="icon" width="20" height="20" aria-hidden="true">
-        <path d="M 5 9 h 10 M 10 5 v 10" />
+        <path d="M 5 3 v 12 M 5 15 l -2 2 M 5 15 l 2 2 M 5 3 l 3 3" />
       </svg>
     </button>
   </div>