feat(server): implement management endpoints and redis sync

Enable full resource management via API and support data plane
synchronization.

- Add CRUD handlers for Providers, Models, and Keys using DTOs
- Implement LogWriter service for asynchronous, batched audit logging
- Update SyncService to snapshot full configuration state to Redis
- Register new API routes and initialize background services
- Add configuration options for logging performance tuning

internal/dto/provider.go

@@ -0,0 +1,9 @@
+package dto
+
+// ProviderDTO defines inbound payload for provider creation/update.
+type ProviderDTO struct {
+    Name    string `json:"name"`
+    Type    string `json:"type"`
+    BaseURL string `json:"base_url"`
+    APIKey  string `json:"api_key"`
+}