fix(knowledge-base): 串接 NEXT_PUBLIC_API_URL 取代相對路徑

- /api/v1/knowledge 改用 process.env.NEXT_PUBLIC_API_URL 前綴
- 確保 Docker build 後能正確連到後端 API，不再打到 Next.js app server

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/app/[locale]/knowledge-base/page.tsx

@@ -114,7 +114,8 @@ export default function KnowledgeBasePage({
       if (searchQuery) params.set('q', searchQuery)
       params.set('limit', '50')
 
-      const res = await fetch(`/api/v1/knowledge?${params}`)
+      const apiBase = process.env.NEXT_PUBLIC_API_URL ?? ''
+      const res = await fetch(`${apiBase}/api/v1/knowledge?${params}`)
       if (res.ok) {
         const data: ListResponse = await res.json()
         setEntries(data.items)