feat(lessons): add lessons from client db

src/components/Math.tsx

@@ -0,0 +1,25 @@
+import React from "react";
+
+/**
+ * Renders a proper stacked fraction with numerator above denominator.
+ * Usage: <Frac n="x² − 1" d="x² − 2x + 1" />
+ */
+export const Frac = ({ n, d }: { n: React.ReactNode; d: React.ReactNode }) => (
+  <span
+    style={{
+      display: "inline-flex",
+      flexDirection: "column",
+      alignItems: "center",
+      verticalAlign: "middle",
+      lineHeight: 1.25,
+      margin: "0 3px",
+    }}
+  >
+    <span
+      style={{ borderBottom: "1.5px solid currentColor", padding: "0 4px 2px" }}
+    >
+      {n}
+    </span>
+    <span style={{ padding: "2px 4px 0" }}>{d}</span>
+  </span>
+);