feat: add interactive conventional commit workflow with jj-lib backend

Replace CLI executor with jj-lib integration, implement full interactive
commit workflow via prompts, and add mock infrastructure for testing.
Add CLI integration tests and error handling tests.

tests/cli.rs

@@ -0,0 +1,99 @@
+use assert_fs::TempDir;
+#[cfg(feature = "test-utils")]
+use jj_cz::{CommitType, Description, MockPrompts, Scope};
+use jj_cz::{CommitWorkflow, Error, JjLib};
+#[cfg(feature = "test-utils")]
+use std::process::Command;
+
+/// Helper to initialize a temporary jj repository
+#[cfg(feature = "test-utils")]
+fn init_jj_repo(temp_dir: &TempDir) {
+    let status = Command::new("jj")
+        .args(["git", "init"])
+        .current_dir(temp_dir)
+        .status()
+        .expect("Failed to initialize jj repository");
+    assert!(status.success(), "jj git init failed");
+}
+
+#[cfg(feature = "test-utils")]
+#[tokio::test]
+async fn test_happy_path_integration() {
+    // T037: Happy path integration test
+    let temp_dir = TempDir::new().unwrap();
+    init_jj_repo(&temp_dir);
+
+    // Create mock prompts that simulate a successful workflow
+    let mock_prompts = MockPrompts::new()
+        .with_commit_type(CommitType::Feat)
+        .with_scope(Scope::empty())
+        .with_description(Description::parse("add new feature").unwrap())
+        .with_confirm(true);
+
+    // Create a mock executor that tracks calls
+    let executor = JjLib::with_working_dir(temp_dir.path());
+    let workflow = CommitWorkflow::with_prompts(executor, mock_prompts);
+
+    let result = workflow.run().await;
+
+    // The workflow should complete successfully
+    assert!(
+        result.is_ok(),
+        "Workflow should complete successfully: {:?}",
+        result
+    );
+}
+
+#[tokio::test]
+async fn test_not_in_repo() {
+    // T038: Not-in-repo integration test
+    let temp_dir = TempDir::new().unwrap();
+    // Don't initialize jj repo
+
+    // Create executor with the temp directory (which is not a jj repo)
+    let executor = JjLib::with_working_dir(temp_dir.path());
+    let workflow = CommitWorkflow::new(executor);
+
+    let result = workflow.run().await;
+
+    // Should fail with NotARepository error
+    assert!(matches!(result, Err(Error::NotARepository)));
+}
+
+#[cfg(feature = "test-utils")]
+#[tokio::test]
+async fn test_cancellation() {
+    // T039: Cancellation integration test
+    // This is tricky to test directly without a TTY
+    // We'll test the error handling path instead
+
+    let temp_dir = TempDir::new().unwrap();
+    init_jj_repo(&temp_dir);
+
+    // Create a mock executor that simulates cancellation
+    struct CancelMock;
+
+    #[async_trait::async_trait(?Send)]
+    impl jj_cz::JjExecutor for CancelMock {
+        async fn is_repository(&self) -> Result<bool, Error> {
+            Ok(true)
+        }
+
+        async fn describe(&self, _message: &str) -> Result<(), Error> {
+            Err(Error::Cancelled)
+        }
+    }
+
+    let executor = CancelMock;
+    let mock_prompts = MockPrompts::new()
+        .with_commit_type(CommitType::Feat)
+        .with_scope(Scope::empty())
+        .with_description(Description::parse("test").unwrap())
+        .with_confirm(true);
+    let workflow = CommitWorkflow::with_prompts(executor, mock_prompts);
+
+    let result = workflow.run().await;
+
+    // Should fail with Cancelled error
+    assert!(matches!(result, Err(Error::Cancelled)));
+}