stage-4: ioc_extraction includes CVE-only cases

The ExampleBuilder guard checked urls/domains/ips/hashes but not cves, so
CISA KEV cases (CVE is their only observable) were silently dropped from the
ioc_extraction dataset. Now they produce CVE-extraction examples.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/psyc/lines/train.py

@@ -62,7 +62,7 @@ class DatasetReport(BaseModel):
 
 def _ex_ioc_extraction(case: Case) -> Optional[Example]:
     obs = case.observables
-    if not (obs.urls or obs.domains or obs.ips or obs.hashes):
+    if not (obs.urls or obs.domains or obs.ips or obs.hashes or obs.cves):
         return None
     threat = case.source_metadata.get("threat", "malware")
     tags = case.source_metadata.get("tags", "")