fix: validate API response in keywords.mjs, delete unused classifier.mjs

- Add res.ok check before parsing Anthropic API response
- Validate data.content[0].text exists before accessing
- Remove classifier.mjs (86 lines of dead code, never imported)

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

lib/keywords.mjs

@@ -52,8 +52,11 @@ Example format: ["query one", "query two", "query three"]`;
     })
   });
 
+  if (!res.ok) throw new Error(`Anthropic API error: ${res.status} ${res.statusText}`);
+
   const data = await res.json();
   if (data.error) throw new Error(data.error.message);
+  if (!data.content?.[0]?.text) throw new Error('Unexpected API response: missing content');
 
   const text = data.content[0].text.trim();
   const clean = text.replace(/```json\n?|\n?```/g, '').trim();