feat(markdown): add PasteChoicePopup component for paste-as choice

frontend/src/components/PasteChoicePopup.tsx

@@ -0,0 +1,106 @@
+/**
+ * PasteChoicePopup — floating popup for paste-as choice.
+ * Shows "Text" / "Markdown" buttons (and optionally "Image").
+ * Auto-dismisses after 5 seconds.
+ */
+
+import React, { useEffect } from 'react';
+
+export type PasteChoice = 'text' | 'markdown' | 'image';
+
+interface PasteChoicePopupProps {
+  x: number;
+  y: number;
+  showImage?: boolean;
+  onChoice: (choice: PasteChoice) => void;
+  onDismiss: () => void;
+}
+
+export default function PasteChoicePopup(props: PasteChoicePopupProps) {
+  const { x, y, showImage, onChoice, onDismiss } = props;
+
+  // Auto-dismiss after 5 seconds
+  useEffect(() => {
+    const timer = setTimeout(onDismiss, 5000);
+    return () => clearTimeout(timer);
+  }, [onDismiss]);
+
+  // Escape to dismiss
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') {
+        e.preventDefault();
+        onDismiss();
+      }
+    };
+    document.addEventListener('keydown', onKey);
+    return () => document.removeEventListener('keydown', onKey);
+  }, [onDismiss]);
+
+  const btnStyle: React.CSSProperties = {
+    background: '#333',
+    border: '1px solid #444',
+    borderRadius: '6px',
+    color: '#ccc',
+    padding: '6px 14px',
+    fontSize: '12px',
+    cursor: 'pointer',
+    fontFamily: 'system-ui, sans-serif',
+    transition: 'background 0.1s',
+  };
+
+  return (
+    <div
+      style={{
+        position: 'absolute',
+        left: x,
+        top: y,
+        transform: 'translate(-50%, -100%)',
+        display: 'flex',
+        gap: '4px',
+        padding: '6px',
+        background: 'rgba(22, 22, 22, 0.96)',
+        border: '1px solid #333',
+        borderRadius: '10px',
+        backdropFilter: 'blur(12px)',
+        boxShadow: '0 4px 20px rgba(0,0,0,0.5)',
+        zIndex: 200,
+        pointerEvents: 'auto',
+      }}
+      onPointerDown={(e) => e.stopPropagation()}
+    >
+      {/* Full-screen backdrop to block canvas interaction while popup is visible */}
+      <div style={{
+        position: 'fixed', top: 0, left: 0, right: 0, bottom: 0,
+        zIndex: -1,
+      }} onClick={onDismiss} />
+      <span style={{ color: '#666', fontSize: '11px', padding: '6px 4px', whiteSpace: 'nowrap' }}>Paste as:</span>
+      {showImage && (
+        <button
+          style={btnStyle}
+          onClick={() => onChoice('image')}
+          onMouseEnter={(e) => { e.currentTarget.style.background = '#444'; }}
+          onMouseLeave={(e) => { e.currentTarget.style.background = '#333'; }}
+        >
+          Image
+        </button>
+      )}
+      <button
+        style={btnStyle}
+        onClick={() => onChoice('text')}
+        onMouseEnter={(e) => { e.currentTarget.style.background = '#444'; }}
+        onMouseLeave={(e) => { e.currentTarget.style.background = '#333'; }}
+      >
+        Text
+      </button>
+      <button
+        style={{ ...btnStyle, background: '#7950f2', color: '#fff', borderColor: '#7950f2' }}
+        onClick={() => onChoice('markdown')}
+        onMouseEnter={(e) => { e.currentTarget.style.background = '#6741d9'; }}
+        onMouseLeave={(e) => { e.currentTarget.style.background = '#7950f2'; }}
+      >
+        Markdown
+      </button>
+    </div>
+  );
+}