Add configurable task limit per column 🚦

File: client/src/components/Board/Column.jsx

WIP limit warns but doesn't PREVENT
adding more tasks 💀 fr!!

Fix: add hard limit option:
const COLUMN_LIMITS = {
backlog: null, // unlimited
inprogress: 5, // max 5
review: 3, // max 3
done: null // unlimited
}

const limit = COLUMN_LIMITS[columnId]
const isAtLimit = limit && tasks.length >= limit

// disable add card button when at limit:
<button
onClick={() => !isAtLimit && onAddTask(columnId)}
className={mt-2 flex items-center gap-2 text-xs px-2 py-1.5 rounded transition ${isAtLimit ? 'text-red-400/50 cursor-not-allowed' : 'text-[#555] hover:text-[#888]'}}>
{isAtLimit
? 🚫 Limit reached (${limit})
: '＋ Add card'}

~12 lines! No backend needed 🎯
Real Kanban WIP limits!! 🔥