Add session persistence and browser functionality

- Implement `StorageManager` for saving, loading, and managing sessions.
- Introduce platform-specific session directories for persistence.
- Add session browser UI for listing, loading, and deleting saved sessions.
- Enable AI-generated descriptions for session summaries.
- Update configurations to support storage settings and description generation.
- Extend README and tests to document and validate new functionality.

crates/owlen-core/src/provider.rs

@@ -87,9 +87,8 @@ impl ProviderRegistry {
         for provider in self.providers.values() {
             match provider.list_models().await {
                 Ok(mut models) => all_models.append(&mut models),
-                Err(e) => {
-                    // Log error but continue with other providers
-                    eprintln!("Failed to get models from {}: {}", provider.name(), e);
+                Err(_) => {
+                    // Continue with other providers
                 }
             }
         }