UI: chat scroll-to-bottom button + FUT-style agent stat cards

[TraX22]

Summary

Two chat/stats UI improvements.

1. Scroll-to-bottom button (Chat)
A floating round button appears in the chat once you scroll up more than ~240px from the latest message, and jumps back to the bottom (smooth) when clicked. It hides itself once you reach the bottom. New Lucide chevron-down icon in the shared icon component.

2. FUT-style agent stat cards (Statistics)
The per-agent stats table is replaced with FIFA/FUT-style cards. Each agent card shows:

• An OVR (0-99) and a role-based position (DEV/GEN/ART/VID).
• A tier by ranking: 1st place → gold, 2nd/3rd → platinum, the rest → bronze (recomputed live as OVRs change).
• Avatar, name, online dot, and the six real stats mapped to FIFA-style attributes (Speed, Completed, Tasks, Success, Reliability, Workload), each a 0-99 rating with a tooltip carrying the real value. Counts are scaled relative to the busiest agent; rate-based ones are absolute percentages.

i18n

New keys in all five locales (en/es/fr/it/pt): chat.scrollToBottom, stats.online, stats.offline, and the six stats.attr* names.

Verification

• pnpm --filter ui build green.
• Chat: verified via headless browser — the button appears on scroll-up, scrolls to the latest message (distance ~3px), and hides at the bottom.
• Stats: verified the six cards render with distinct OVRs/tiers (gold/platinum/bronze) and localized attribute names (es/en).

Out of scope

• No backend/API changes; UI only.