examples: add 6 new over-engineering survivors + platform-native guide (#109)

New examples (examples/):
- modal-dialog: <dialog> vs Radix/react-modal
- url-params: URLSearchParams vs query-string
- number-formatting: Intl.NumberFormat vs numeral
- infinite-scroll: IntersectionObserver vs react-infinite-scroll-component
- deep-clone: structuredClone vs lodash.cloneDeep / JSON hack
- group-by: Object.groupBy vs lodash.groupBy

New doc (docs/platform-native.md):
Comprehensive reference of platform-native solutions across HTML elements,
CSS, Browser APIs, Node.js stdlib, Python stdlib, and database features.
Covers 60+ cases where the platform already has what developers reach for
a package to do.

examples/infinite-scroll.md

@@ -0,0 +1,58 @@
+# Infinite Scroll
+
+**Task:** "Load more items when the user scrolls to the bottom."
+
+## Without Ponytail
+
+```bash
+npm install react-infinite-scroll-component
+```
+
+```jsx
+import InfiniteScroll from "react-infinite-scroll-component";
+
+export function Feed({ items, fetchMore, hasMore }) {
+  return (
+    <InfiniteScroll
+      dataLength={items.length}
+      next={fetchMore}
+      hasMore={hasMore}
+      loader={<Spinner />}
+      endMessage={<p>No more items</p>}
+      scrollThreshold={0.9}
+    >
+      {items.map(item => <Card key={item.id} item={item} />)}
+    </InfiniteScroll>
+  );
+}
+```
+
+A dependency to watch scroll position and fire a callback.
+
+## With Ponytail
+
+```jsx
+// ponytail: IntersectionObserver does this, no scroll listener needed
+import { useEffect, useRef } from "react";
+
+export function Feed({ items, fetchMore, hasMore }) {
+  const sentinel = useRef(null);
+
+  useEffect(() => {
+    const observer = new IntersectionObserver(([entry]) => {
+      if (entry.isIntersecting && hasMore) fetchMore();
+    });
+    if (sentinel.current) observer.observe(sentinel.current);
+    return () => observer.disconnect();
+  }, [hasMore, fetchMore]);
+
+  return (
+    <>
+      {items.map(item => <Card key={item.id} item={item} />)}
+      <div ref={sentinel} />
+    </>
+  );
+}
+```
+
+**1 dependency → 0 dependencies.** `IntersectionObserver` fires only when the sentinel enters the viewport — no scroll event, no throttling, no jank. Ships in every browser. The library wraps exactly this API.