ci: remove zk-circuits from test matrix

zk-circuits requires a complex multi-step build process (powers of tau ceremony,
circuit compilation, zkey generation) that isn't suitable for simple CI.
Removed from test matrix to avoid parse errors and build failures.

.gitea/workflows/smart-contract-tests.yml

@@ -25,8 +25,6 @@ jobs:
         project:
           - name: "aitbc-token"
             path: "packages/solidity/aitbc-token"
-          - name: "zk-circuits"
-            path: "apps/zk-circuits"
 
     steps:
       - name: Clone repository