chore(deps): docs in-range updates, pin zod, override xmldom

Next 16.3.5 and React 19.3 in docs/, plus the transitive refresh that came
with them (mermaid 11.17, katex 0.16.47, shiki 3.23, styled-components 6.5).

Two overrides were needed:

- zod ~4.3.6. nextra 4.6.1 declares `zod: ^4.1.12` but its MDX prop
  validation breaks on zod >= 4.4.0, failing prerender for every page with
  "Invalid input: expected nonoptional, received undefined -> at children".
  Bisected: 4.3.6 builds, 4.4.0 through 4.6.2 all fail. nextra 4.6.1 is the
  latest release, so there is no upstream fix to take yet. Drop this pin
  once nextra ships one.

- @xmldom/xmldom ^0.9.12. speech-rule-engine 4.1.4 (via mathjax-full ->
  better-react-mathjax -> nextra) pins xmldom at exactly 0.9.10, so
  `npm audit fix` cannot reach it. 0.9.12 clears 13 advisories including
  GHSA-6gmq-8vp8-gcm6 (high).

Docs build passes, 48 pages indexed, 0 advisories.

docs/package.json

@@ -9,15 +9,19 @@
   "dependencies": {
     "@vercel/analytics": "^2.0.1",
     "docsgpt-react": "^0.7.1",
-    "next": "^16.3.0",
+    "next": "^16.3.5",
     "next-themes": "^0.4.6",
     "nextra": "^4.6.1",
     "nextra-theme-docs": "^4.6.1",
-    "react": "^19.2.8",
-    "react-dom": "^19.2.8"
+    "react": "^19.3.0",
+    "react-dom": "^19.3.0"
   },
   "devDependencies": {
     "pagefind": "^1.5.2",
     "typescript": "^6.0.3"
+  },
+  "overrides": {
+    "@xmldom/xmldom": "^0.9.12",
+    "zod": "~4.3.6"
   }
 }