[BUG]: Many controls lack screen reader labels (#1023)

* Add accessible labels for back and continue buttons in onboarding flow

* Add accessible label to stop generating button

* Accessible labels for chat history actions (thumb up/down and copy)

* Accessible labels for social links in footer

* Accessible labels for home and settings links

* * Accessible labels for home, show sidebar (mobile), and workspace and thread lists.

* Implemented ARIA markup to programmatically indicate current selection and group/list association.