## Summary - keep short Chat transcripts bottom-aligned without negative flex overflow - make older messages reachable when a transcript exceeds the pane - cover desktop and compact/mobile layouts with a Playwright regression

## Root cause The transcript stack used justify-end. Once its content exceeded the scroll container, flexbox aligned the overflow above the scroll origin, so setting scrollTop to zero still left older messages offscreen. A first-child auto margin preserves bottom alignment only while free space exists and collapses safely for tall content.

## Verification - bun test apps/web/src/chat (51 pass) - bun run types - bun run ci - Playwright: chat keeps the start of a tall transcript reachable across layouts