* fix(chat): use streamdown code controls for markdown blocks * fix(chat): keep code block actions in header row and body scrollable * fix(chat): allow horizontal scrolling in virtualized code output * fix(chat): preserve mobile horizontal scrolling in code blocks * fix: refine chat code block header and actions styling * fix: restore themed code highlighting and polish chat code blocks --------- Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>