feat: major dashboard overhaul and polish

- Switched from mock data to real backend APIs.
- Implemented unified ApiClient for consistent frontend data fetching.
- Refactored dashboard structure and styles for a modern SaaS aesthetic.
- Fixed Axum 0.8+ routing and parameter syntax issues.
- Implemented real client creation/deletion and provider health monitoring.
- Synchronized WebSocket event structures between backend and frontend.

src/providers/mod.rs

@@ -86,6 +86,10 @@ impl ProviderManager {
             .find(|p| p.name() == name)
             .map(|p| Arc::clone(p))
     }
+
+    pub fn get_all_providers(&self) -> Vec<Arc<dyn Provider>> {
+        self.providers.clone()
+    }
 }
 
 // Create placeholder provider implementations