fix: clear error on import success and enable noNonNullAssertion warning

- Clear error state in importGitLabIssues when result.success is true
- Change biome noNonNullAssertion rule from 'off' to 'warn'

Co-Authored-By: Claude Opus 4.6 <[email protected]>

apps/desktop/biome.jsonc

@@ -46,7 +46,7 @@
         "useNodejsImportProtocol": "off",
         "useImportType": "off",
         "useTemplate": "off",
-        "noNonNullAssertion": "off"
+        "noNonNullAssertion": "warn"
       },
       "suspicious": {
         "recommended": true,

apps/desktop/src/renderer/stores/gitlab/issues-store.ts

@@ -158,6 +158,7 @@ export async function importGitLabIssues(
   try {
     const result = await window.electronAPI.importGitLabIssues(projectId, issueIids);
     if (result.success) {
+      store.setError(null); // Clear error on success
       return true;
     } else {
       store.setError(result.error || 'Failed to import GitLab issues');