feat(surface): make attack surface first-class in the finding pipeline

tests/lang_detect_probes.rs

@@ -55,6 +55,7 @@ mod lang_detect {
             }),
             rank_score: None,
             rank_reason: None,
+            exposure: None,
             suppressed: false,
             suppression: None,
             triage_state: "open".to_string(),