fix(spark-analytics): increase NIM timeout and trim max_tokens to avoid read timeouts

70B model at 30-50 tok/s was exceeding the 30s urllib timeout for larger
outputs. Raise server timeout to 60s, add browser AbortController at 65s
so the UI fails gracefully. Trim max_tokens (row: 300, dataset: 512) to
keep generation well inside the window.

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

spark-analytics/base/webview.yaml

@@ -182,11 +182,19 @@ data:
     }
 
     async function nimFetch(payload) {
-      const resp = await fetch('/explain', {
-        method: 'POST',
-        headers: { 'Content-Type': 'application/json' },
-        body: JSON.stringify(payload),
-      });
+      const ctrl = new AbortController();
+      const tid = setTimeout(() => ctrl.abort(), 65000);
+      let resp;
+      try {
+        resp = await fetch('/explain', {
+          method: 'POST',
+          headers: { 'Content-Type': 'application/json' },
+          body: JSON.stringify(payload),
+          signal: ctrl.signal,
+        });
+      } finally {
+        clearTimeout(tid);
+      }
       if (resp.status === 429) {
         const retryAfter = parseInt(resp.headers.get('Retry-After') || '10', 10);
         const err = new Error('Rate limited — retry in ' + retryAfter + 's');
@@ -494,7 +502,7 @@ data:
                         f"Entry to analyze: {row_desc}\n\n"
                         "Provide a detailed, chess-specific analysis of this entry."
                     )
-                    max_tokens = 600
+                    max_tokens = 300
                 else:
                     sample = dataset.get("sample", [])
                     rows_text = "\n".join(
@@ -514,7 +522,7 @@ data:
                         f"Top 10 entries:\n{rows_text}\n\n"
                         "Analyze each entry."
                     )
-                    max_tokens = 1024
+                    max_tokens = 512
 
                 payload = json.dumps({
                     "model": "meta/llama-3.3-70b-instruct",
@@ -536,7 +544,7 @@ data:
                     method="POST",
                 )
                 try:
-                    with urllib.request.urlopen(req, timeout=30) as r:
+                    with urllib.request.urlopen(req, timeout=60) as r:
                         nim_data = json.loads(r.read())
                     text = nim_data.get("choices", [{}])[0].get("message", {}).get("content", "(no response)")
                     self._send_json({"text": text})