🤲 a11y: Sidebar Text Contrast (#3665)

* fix: use theme class for valid contrast for light/dark, conversation group names, fix type issues

* fix: searchbar text contrast styling, closes #3469

* style: add theming for prompt cards, fix a11y contrast issues

* a11y: address placeholder text contrast issues in LLM controls section

* chore: Add conditional check for pull request repository in a11y workflow

* style: Update text color contrast to WCAG standard for placeholder and focus states in AssistantPanel components

client/src/components/Conversations/Conversations.tsx

@@ -10,7 +10,7 @@ const Conversations = ({
   moveToTop,
   toggleNav,
 }: {
-  conversations: TConversation[];
+  conversations: Array<TConversation | null>;
   moveToTop: () => void;
   toggleNav: () => void;
 }) => {
@@ -33,15 +33,15 @@ const Conversations = ({
           {groupedConversations.map(([groupName, convos]) => (
             <div key={groupName}>
               <div
+                className="text-text-secondary"
                 style={{
-                  color: '#535353',
                   fontSize: '0.7rem',
                   marginTop: '20px',
                   marginBottom: '5px',
                   paddingLeft: '10px',
                 }}
               >
-                {localize(groupName) || groupName}
+                {localize(groupName) ?? groupName}
               </div>
               {convos.map((convo, i) => (
                 <Convo