TUI — flicker-free rendering (synchronized output)

Ink repaints the whole frame on every animation tick (every 120ms while runs are live), which on most terminals causes visible full-screen flicker. Every Ink frame write is wrapped in DEC 2026 synchronized-update markers (ESC[?2026h … ESC[?2026l, via src/tui/syncOutput.ts) so the terminal composites each frame atomically and repaints only the cells that changed — animation stays confined to the area that animates. Terminals without DEC 2026 support ignore the markers (harmless no-op). Applies to all three Ink front-ends: cyberine agents, cyberine chat, and the resume session picker.