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/auth/oauth.rs

@@ -0,0 +1,53 @@
+//! Pure OAuth entities — no HTTP or persistence logic.
+//!
+//! # Components
+//!
+//! - [`OAuthToken`] — access token with optional refresh token, epoch expiry
+//! - [`OAuthConfig`] — provider configuration (auth URL, token URL, client id,
+//!   optional client secret, scopes)
+use serde::{Deserialize, Serialize};
+
+/// An OAuth 2.0 access token with optional refresh token and absolute
+/// expiry time (epoch seconds).
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OAuthToken {
+    /// The OAuth 2.0 access token string.
+    pub access_token: String,
+    /// Optional refresh token for long-lived access.
+    pub refresh_token: Option<String>,
+    /// Absolute expiry timestamp (epoch seconds since UNIX_EPOCH).
+    pub expires_at: u64,
+    /// Token type, e.g. `"Bearer"`.
+    pub token_type: String,
+}
+
+/// Static configuration for an OAuth provider.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OAuthConfig {
+    /// Authorization endpoint URL.
+    pub auth_url: String,
+    /// Token exchange endpoint URL.
+    pub token_url: String,
+    /// OAuth client identifier.
+    pub client_id: String,
+    /// Optional client secret (not all flows require it).
+    pub client_secret: Option<String>,
+    /// Space-separated list of requested scopes.
+    pub scopes: Vec<String>,
+}
+
+impl Default for OAuthConfig {
+    fn default() -> Self {
+        OAuthConfig {
+            auth_url: String::new(),
+            token_url: String::new(),
+            client_id: String::new(),
+            client_secret: None,
+            scopes: vec![
+                "openid".to_string(),
+                "profile".to_string(),
+                "email".to_string(),
+            ],
+        }
+    }
+}