feat: content fetch, sitemap fixes, remove oidcAuthFlow

- Add contentFetchFlow() to proxy (FR-001 through FR-012)
- Add extractArticleBody() helper with vkm:articleBody / articleBody fallback
- Dynamic proxyBaseUrl derivation from x-forwarded-proto/host headers
- Forward query/size/category params on /sitemap.xml requests
- Add Accept: application/ld+json header to content API calls
- Remove oidcAuthFlow() - unmatched requests now return 404 Not Found
- Fix xmlbuilder2 import: default import, call as xmlbuilder2.create(...)
- Version bump 0.2.0 → 0.3.0
- 45/45 tests passing

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "kme-content-adapter",
-  "version": "0.2.0",
+  "version": "0.3.0",
   "description": "HTTP proxy adapter to search and export documents from KME",
   "type": "module",
   "main": "src/server.js",