feat: add Ask ChatGPT toolbar action

options/options.html

@@ -13,6 +13,12 @@
   ChatGPT.
 </p>
 
+<p class="intro">
+  Click the <strong>Ask ChatGPT</strong> toolbar button to ask about selected
+  text, or open a blank chat when nothing is selected. The button works in
+  every context-menu mode and follows your settings below.
+</p>
+
 <form id="settings" autocomplete="off">
   <div class="field">
     <label for="contextMenuMode">Context menu</label>
@@ -71,7 +77,7 @@
   <div class="field">
     <label for="promptTemplate">Prompt template</label>
     <input type="text" id="promptTemplate" spellcheck="false" />
-    <p class="hint"><code>{query}</code> is replaced with your selected text. Used by Ask normally, Simple mode, and the keyboard shortcut. Other advanced actions use their own prompts.</p>
+    <p class="hint"><code>{query}</code> is replaced with your selected text. Used by Ask normally, Simple mode, the toolbar button, and the keyboard shortcut. Other advanced actions use their own prompts.</p>
   </div>
 
   <div class="actions">
@@ -92,7 +98,7 @@
     <a href="https://support.mozilla.org/en-US/kb/change-your-default-search-settings-firefox" target="_blank" rel="noopener noreferrer">Firefox search settings guide</a>.
   </p>
   <p>
-    The settings above apply to the right-click menu and keyboard shortcut;
+    The settings above apply to the right-click menu, toolbar button, and keyboard shortcut;
     address-bar searches use Firefox’s search engine settings.
     Restore defaults only resets extension settings, including the prompt
     template; it does not change Firefox’s search engine or keyboard shortcut.