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/url-params.md

@@ -0,0 +1,41 @@
+# URL Parameters
+
+**Task:** "Parse and build URL query strings."
+
+## Without Ponytail
+
+```bash
+npm install query-string
+# 4.5 kB gzipped, 3.5M downloads/week
+```
+
+```js
+import qs from "query-string";
+
+// Parse
+const params = qs.parse(location.search);
+// → { page: "2", sort: "name", tags: ["js", "css"] }
+
+// Build
+const url = qs.stringify({ page: 2, sort: "name", tags: ["js", "css"] });
+// → "page=2&sort=name&tags=js&tags=css"
+```
+
+## With Ponytail
+
+```js
+// ponytail: URLSearchParams does this
+const params = new URLSearchParams(location.search);
+
+// Read
+params.get("page");         // "2"
+params.getAll("tags");      // ["js", "css"]
+
+// Build
+const out = new URLSearchParams({ page: 2, sort: "name" });
+out.append("tags", "js");
+out.append("tags", "css");
+out.toString(); // "page=2&sort=name&tags=js&tags=css"
+```
+
+**1 dependency → 0 dependencies.** `URLSearchParams` is in every browser and in Node.js since v10. It handles encoding, repeated keys, and iteration. The package was a polyfill for an API that has shipped everywhere for years.