fix(deps): bump undici override to 7.28.0 to clear high-severity audit

The pnpm production audit fails on GHSA-vmh5-mc38-953g (undici TLS
certificate validation bypass via SOCKS5 ProxyAgent), pulled in
transitively through apps/docs > cheerio > undici. The existing override
pinned undici to 7.24.0, which is still within the vulnerable range
(>=7.23.0 <7.28.0). Bump the override to the patched 7.28.0.

Author: amilz

package.json

@@ -66,7 +66,7 @@
       "svgo@>=3.0.0 <3.3.3": "3.3.3",
       "tar@<7.5.11": "7.5.11",
       "tmp@<0.2.6": "0.2.6",
-      "undici@>=7.0.0 <7.24.0": "7.24.0",
+      "undici@>=7.0.0 <7.28.0": "7.28.0",
       "vite@>=7.0.0 <=7.3.4": "7.3.5",
       "ws@>=7.0.0 <7.5.11": "7.5.11",
       "ws@>=8.0.0 <8.21.0": "8.21.0"