Add local proxy server for AI draft button; point button at /api/claude

tools/field-problem-workshop.html

@@ -653,7 +653,7 @@ document.getElementById('btnAddBc').addEventListener('click', ()=>{
 
 /* ===== AI: draft breadcrumb fields from methodology ===== */
 async function callClaude(prompt){
-  const response = await fetch("https://api.anthropic.com/v1/messages", {
+  const response = await fetch("/api/claude", {
     method: "POST",
     headers: { "Content-Type": "application/json" },
     body: JSON.stringify({ model: "claude-sonnet-4-6", max_tokens: 1000, messages: [{ role: "user", content: prompt }] })