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/infrastructure/src/persistence/iam/oauth_repo.rs

@@ -0,0 +1,39 @@
+//! Filesystem-backed `OAuthRepository` implementation.
+//!
+//! Tokens are stored as a single JSON file with write-then-rename + fsync
+//! for crash safety, and restrictive owner-only mode `0o600` on Unix.
+
+use std::path::Path;
+
+use zesdex_domain::auth::{OAuthRepository, OAuthToken, RepositoryError};
+
+use crate::utils::write_json_atomic;
+
+/// Concrete filesystem OAuth token repository.
+#[derive(Debug, Clone, Default)]
+pub struct FileSystemOAuthRepository;
+
+impl FileSystemOAuthRepository {
+    pub fn new() -> Self {
+        FileSystemOAuthRepository
+    }
+}
+
+impl OAuthRepository for FileSystemOAuthRepository {
+    fn save_token(&self, path: &Path, token: &OAuthToken) -> Result<(), RepositoryError> {
+        if let Some(parent) = path.parent() {
+            std::fs::create_dir_all(parent)?;
+        }
+        write_json_atomic(path, token, Some(0o600))?;
+        Ok(())
+    }
+
+    fn load_token(&self, path: &Path) -> Result<Option<OAuthToken>, RepositoryError> {
+        if !path.exists() {
+            return Ok(None);
+        }
+        let data = std::fs::read_to_string(path)?;
+        let token: OAuthToken = serde_json::from_str(&data)?;
+        Ok(Some(token))
+    }
+}