feat: stratagem icons, session summary, queue preview, UX polish

- Download 65 SVG icons from community repo (scripts/download-icons.js)
- Gold CSS filter on all icons to match game theme
- Session summary modal with score/accuracy/top stratagems
- Queue preview strip (next 3 stratagems with icons)
- Score popup animation, icon shake on wrong input
- Icons in history, leaderboard, and best-per-stratagem tables
- server.js: icon fields on all stratagems, ELO in lobby-update WS events

public/icons/stalwart.svg

@@ -0,0 +1 @@
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