fix: align CR format with broker CompleteRequest schema

- Add session_id field to CrEvidence (broker expects it)
- Change merkle_root to Option<String> (null vs empty string)
- Change events to Vec<serde_json::Value> (broker expects list[dict])
- Fixes 422 Unprocessable Entity on CR posting

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

libgsh/src/cr.rs

@@ -17,8 +17,9 @@ pub struct CrRequest {
 
 #[derive(Serialize)]
 pub struct CrEvidence {
-    pub events: Vec<String>,
-    pub merkle_root: String,
+    pub session_id: Option<String>,
+    pub events: Vec<serde_json::Value>,
+    pub merkle_root: Option<String>,
 }
 
 #[derive(Serialize)]
@@ -77,8 +78,9 @@ pub fn post_cr(client: &Client, base: &str, ac_id: &str, outcome: &str) -> CrRes
             outcome: outcome.into(),
             completed_at: now,
             chronicle_evidence: CrEvidence {
+                session_id: if session_id.is_empty() { None } else { Some(session_id.clone()) },
                 events: vec![],
-                merkle_root: String::new(),
+                merkle_root: None,
             },
             behavioral_attestation: CrAttestation {
                 status: "unavailable".into(),