feat(tui): add usage overlay and sidebar for displaying usage statistics and tasks

feat(tui): implement status bar with connection and turn state indicators
feat(tui): create workflow panel for agent status and progress visualization
feat(web): introduce web frontend interface with static file serving
feat(ws): add WebSocket interface for real-time communication and session management

apps/domain/src/cms/error.rs

@@ -0,0 +1,51 @@
+//! Domain error types for the CMS module.
+//!
+//! Typed error enums for repository and service operations.
+//!
+//! # Components
+//!
+//! - [`RepositoryError`] — persistence-layer errors (not found, conflict, I/O)
+//! - [`ServiceError`] — use-case / orchestration errors (invalid input, generic)
+
+use std::fmt;
+
+use crate::error::DomainError;
+
+/// Shared repository error type for CMS persistence operations.
+pub type RepositoryError = DomainError;
+
+/// Errors from service / use-case operations in the CMS domain.
+#[derive(Debug)]
+pub enum ServiceError {
+    /// A repository operation failed.
+    Repository(DomainError),
+    /// The provided input is invalid.
+    InvalidInput(String),
+    /// A generic error with a message.
+    Other(String),
+}
+
+impl From<DomainError> for ServiceError {
+    fn from(err: DomainError) -> Self {
+        ServiceError::Repository(err)
+    }
+}
+
+impl fmt::Display for ServiceError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ServiceError::Repository(err) => write!(f, "repository error: {err}"),
+            ServiceError::InvalidInput(msg) => write!(f, "invalid input: {msg}"),
+            ServiceError::Other(msg) => write!(f, "{msg}"),
+        }
+    }
+}
+
+impl std::error::Error for ServiceError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            ServiceError::Repository(err) => Some(err),
+            _ => None,
+        }
+    }
+}