fix(canvas): 画布 - 防止旧内容覆盖并支持版本历史恢复

backend/internal/database/migrations.go

@@ -11,7 +11,7 @@ import (
 	"gorm.io/gorm"
 )
 
-const CurrentSchemaVersion int64 = 15
+const CurrentSchemaVersion int64 = 16
 
 const baselineSchemaChecksum = "sha256:open-ai-canvas-schema-v1-20260830"
 const schemaMigrationAppliedAtIndexChecksum = "sha256:schema-migrations-applied-at-index-v2-20260830"
@@ -67,6 +67,9 @@ var schemaMigrations = []migration{
 	{version: 15, name: "agent_profiles", checksum: "sha256:agent-profiles-v15-20260914", apply: func(tx *gorm.DB) error {
 		return tx.AutoMigrate(&model.AgentProfile{})
 	}},
+	{version: 16, name: "canvas_revision_history", checksum: "sha256:canvas-revision-history-v16", apply: func(tx *gorm.DB) error {
+		return tx.AutoMigrate(&model.CanvasProject{}, &model.CanvasSnapshot{}, &model.CanvasSnapshotResource{})
+	}},
 }
 
 func migrateSchemaV14(tx *gorm.DB) error {