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/model/models.go

@@ -1,6 +1,8 @@
 package model
 
 import (
+	"time"
+
 	"gorm.io/gorm"
 )
 
@@ -34,12 +36,16 @@ type Key struct {
 // Provider remains the same.
 type Provider struct {
 	gorm.Model
-	Name    string `gorm:"not null" json:"name"`
-	Type    string `gorm:"not null" json:"type"` // openai, anthropic, etc.
-	BaseURL string `json:"base_url"`
-	APIKey  string `json:"api_key"`
-	Group   string `gorm:"default:'default'" json:"group"` // routing group/tier
-	Models  string `json:"models"`                         // comma-separated list of supported models (e.g. "gpt-4,gpt-3.5-turbo")
+	Name      string     `gorm:"not null" json:"name"`
+	Type      string     `gorm:"not null" json:"type"` // openai, anthropic, etc.
+	BaseURL   string     `json:"base_url"`
+	APIKey    string     `json:"api_key"`
+	Group     string     `gorm:"default:'default'" json:"group"`         // routing group/tier
+	Models    string     `json:"models"`                                 // comma-separated list of supported models (e.g. "gpt-4,gpt-3.5-turbo")
+	Status    string     `gorm:"size:50;default:'active'" json:"status"` // active, auto_disabled, manual_disabled
+	AutoBan   bool       `gorm:"default:true" json:"auto_ban"`           // whether DP-triggered disable is allowed
+	BanReason string     `gorm:"size:255" json:"ban_reason"`             // reason for current disable
+	BanUntil  *time.Time `json:"ban_until"`                              // optional TTL for disable
 }
 
 // Model remains the same.