feat(provider): add status and banning mechanism

Introduce fields for managing provider status (active, auto_disabled,
manual_disabled) and banning logic.

- Add Status, AutoBan, BanReason, and BanUntil to Provider model and DTO
- Update CreateProvider handler to process new fields with defaults
- Extend sync service to propagate status and ban information in snapshots
- Serialize BanUntil as Unix timestamp for sync compatibility

internal/dto/provider.go

@@ -1,11 +1,17 @@
 package dto
 
+import "time"
+
 // 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"`
-	Group   string   `json:"group"`
-	Models  []string `json:"models"` // List of supported model names
+	Name      string    `json:"name"`
+	Type      string    `json:"type"`
+	BaseURL   string    `json:"base_url"`
+	APIKey    string    `json:"api_key"`
+	Group     string    `json:"group"`
+	Models    []string  `json:"models"` // List of supported model names
+	Status    string    `json:"status"`
+	AutoBan   *bool     `json:"auto_ban,omitempty"`
+	BanReason string    `json:"ban_reason,omitempty"`
+	BanUntil  time.Time `json:"ban_until,omitempty"`
 }