Add static class names to UI elements for easier customization (#4421)

* Initial plan

* Add static class names to UI elements for easier customization

Co-authored-by: gabek <414923+gabek@users.noreply.github.com>

* Add unique DOM element IDs for easier customization targeting

Co-authored-by: gabek <414923+gabek@users.noreply.github.com>

* Remove duplicate class names, keep only IDs for UI element targeting

Co-authored-by: gabek <414923+gabek@users.noreply.github.com>

* Revert chat input field ID to original value

Co-authored-by: gabek <414923+gabek@users.noreply.github.com>

* Remove unnecessary nested spans and revert Button ID to original value

Co-authored-by: gabek <414923+gabek@users.noreply.github.com>

* Standardize ID names to follow owncast-{element-description}-{type} pattern

Co-authored-by: gabek <414923+gabek@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: gabek <414923+gabek@users.noreply.github.com>
Co-authored-by: Gabe Kangas <gabek@real-ity.com>

web/components/ui/Header/Header.tsx

@@ -64,7 +64,9 @@ export const Header: FC<HeaderComponentProps> = ({ name, chatAvailable, chatDisa
           title={t('Chat will be available when the stream is live.')}
           placement="left"
         >
-          <span className={styles.chatOfflineText}>{t('Chat is offline')}</span>
+          <span className={styles.chatOfflineText} id="owncast-chat-offline-text">
+            {t('Chat is offline')}
+          </span>
         </Tooltip>
       )}
     </header>