feat: add shared ContextMenu component

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/common/ContextMenu.tsx

@@ -0,0 +1,104 @@
+import { useEffect, useRef, useCallback } from 'react'
+import { cn } from '@/lib/utils'
+
+export interface ContextMenuPosition {
+  x: number
+  y: number
+}
+
+export interface ContextMenuItem {
+  id: string
+  label: string
+  icon?: React.ReactNode
+  onClick: () => void
+  variant?: 'default' | 'danger'
+  separator?: boolean
+}
+
+interface ContextMenuProps {
+  position: ContextMenuPosition
+  items: ContextMenuItem[]
+  onClose: () => void
+}
+
+export function ContextMenu({ position, items, onClose }: ContextMenuProps) {
+  const menuRef = useRef<HTMLDivElement>(null)
+
+  const handleClickOutside = useCallback(
+    (e: MouseEvent) => {
+      if (menuRef.current && !menuRef.current.contains(e.target as Node)) {
+        onClose()
+      }
+    },
+    [onClose]
+  )
+
+  const handleKeyDown = useCallback(
+    (e: KeyboardEvent) => {
+      if (e.key === 'Escape') onClose()
+    },
+    [onClose]
+  )
+
+  useEffect(() => {
+    document.addEventListener('mousedown', handleClickOutside)
+    document.addEventListener('keydown', handleKeyDown)
+    return () => {
+      document.removeEventListener('mousedown', handleClickOutside)
+      document.removeEventListener('keydown', handleKeyDown)
+    }
+  }, [handleClickOutside, handleKeyDown])
+
+  // Adjust position to stay within viewport
+  useEffect(() => {
+    if (!menuRef.current) return
+    const rect = menuRef.current.getBoundingClientRect()
+    const el = menuRef.current
+    if (position.x + rect.width > window.innerWidth) {
+      el.style.left = `${position.x - rect.width}px`
+    }
+    if (position.y + rect.height > window.innerHeight) {
+      el.style.top = `${position.y - rect.height}px`
+    }
+  }, [position])
+
+  return (
+    <div
+      ref={menuRef}
+      style={{
+        position: 'fixed',
+        zIndex: 100,
+        left: position.x,
+        top: position.y,
+      }}
+      className="min-w-[200px] rounded-xl border border-border bg-card p-1 shadow-lg backdrop-blur-md"
+    >
+      {items.map((item) => (
+        <div key={item.id}>
+          {item.separator && (
+            <div className="my-1 border-t border-border" />
+          )}
+          <button
+            onClick={() => {
+              item.onClick()
+              onClose()
+            }}
+            className={cn(
+              'flex w-full items-center gap-2 rounded-lg px-3 py-2 text-sm transition-colors',
+              item.variant === 'danger'
+                ? 'text-rose-400 hover:bg-rose-500/10'
+                : 'text-foreground hover:bg-[rgba(255,255,255,0.06)]'
+            )}
+          >
+            {item.icon && (
+              <span className="flex h-4 w-4 items-center justify-center text-muted-foreground">
+                {item.icon}
+              </span>
+            )}
+            {item.label}
+          </button>
+        </div>
+      ))}
+    </div>
+  )
+}