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.

src/error.rs

@@ -1,6 +1,6 @@
 use crate::commit::types::{CommitMessageError, DescriptionError, ScopeError};
 
-#[derive(Debug, thiserror::Error)]
+#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
 pub enum Error {
     // Domain errors
     #[error("Invalid scope: {0}")]
@@ -50,33 +50,3 @@ impl From<std::io::Error> for Error {
         Self::FailedGettingCurrentDir
     }
 }
-
-impl From<jj_lib::config::ConfigGetError> for Error {
-    fn from(_: jj_lib::config::ConfigGetError) -> Self {
-        Self::FailedReadingConfig
-    }
-}
-
-impl From<jj_lib::repo::RepoLoaderError> for Error {
-    fn from(error: jj_lib::repo::RepoLoaderError) -> Self {
-        Self::JjOperation {
-            context: format!("Failed to load repository: {}", error),
-        }
-    }
-}
-
-impl From<jj_lib::backend::BackendError> for Error {
-    fn from(error: jj_lib::backend::BackendError) -> Self {
-        Self::JjOperation {
-            context: format!("Backend operation failed: {}", error),
-        }
-    }
-}
-
-impl From<jj_lib::transaction::TransactionCommitError> for Error {
-    fn from(error: jj_lib::transaction::TransactionCommitError) -> Self {
-        Self::JjOperation {
-            context: format!("Transaction commit failed: {}", error),
-        }
-    }
-}