feat(*): 云端 Agent - 增强画布上下文读取并接入 Gemini 缓存

backend/internal/model/cloud_agent_gemini_cache.go

@@ -0,0 +1,19 @@
+package model
+
+import "time"
+
+// CloudAgentGeminiCache records an official Gemini CachedContent resource.
+// The upstream credential is never stored; CredentialHash is only an identity
+// component used to prevent reusing a cache across different credentials.
+type CloudAgentGeminiCache struct {
+	ID             string    `gorm:"primaryKey;size:80"`
+	UserID         string    `gorm:"index;uniqueIndex:idx_cloud_agent_gemini_cache_user_key;size:36;not null"`
+	CacheKey       string    `gorm:"uniqueIndex:idx_cloud_agent_gemini_cache_user_key;size:64;not null"`
+	BaseURL        string    `gorm:"size:500;not null"`
+	Model          string    `gorm:"size:200;not null"`
+	CredentialHash string    `gorm:"size:64;not null"`
+	ResourceName   string    `gorm:"size:300;not null"`
+	ExpireTime     time.Time `gorm:"index;not null"`
+	CreatedAt      time.Time
+	UpdatedAt      time.Time
+}