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/key.go

@@ -0,0 +1,10 @@
+package dto
+
+// KeyDTO defines payload for key creation/update.
+type KeyDTO struct {
+    ProviderID uint    `json:"provider_id"`
+    KeySecret  string  `json:"key_secret"`
+    Balance    float64 `json:"balance"`
+    Status     string  `json:"status"`
+    Weight     int     `json:"weight"`
+}