fix: stub marketplace payment check, fix build errors

Replace handle_lnd_lookupinvoice (doesn't exist) with stub.
Payment verification deferred to Y4-02 marketplace implementation.

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

core/archipelago/src/api/rpc/marketplace.rs

@@ -179,19 +179,10 @@ impl RpcHandler {
             .and_then(|v| v.as_str())
             .ok_or_else(|| anyhow::anyhow!("Missing r_hash"))?;
 
-        // Check invoice status via LND
-        let lookup_params = serde_json::json!({ "r_hash": r_hash });
-        let lookup_result = self
-            .handle_lnd_lookupinvoice(Some(lookup_params))
-            .await;
-
-        let paid = match lookup_result {
-            Ok(ref inv) => inv
-                .get("settled")
-                .and_then(|v| v.as_bool())
-                .unwrap_or(false),
-            Err(_) => false,
-        };
+        // Check invoice status — stub until LND lookup is implemented
+        // TODO: Add lnd.lookupinvoice RPC endpoint for real payment verification
+        let paid = false; // Payment verification pending LND integration
+        let _ = r_hash; // Used when LND lookup is available
 
         Ok(serde_json::json!({
             "r_hash": r_hash,