fix(model): correct idx_created_at_id index column order to (created_at, id) (#5191)

The idx_created_at_id composite index on the logs table was defined as
(id, created_at) because the GORM `priority` values on Id and CreatedAt were
swapped. Since `id` is the auto-increment primary key, a secondary composite
index leading with `id` is redundant with the PK and cannot accelerate
`created_at` range scans (a range column must sit at the index prefix).

This defeats the common log-listing queries
(`WHERE created_at BETWEEN ? AND ? ORDER BY id DESC LIMIT n` in
GetAllLogs/GetUserLogs) that the index name implies it should serve — the
optimizer falls back to scanning the primary key, degrading to near full-table
scans on large logs tables.

Swap the priorities so the column order becomes (created_at, id), matching the
index name and its intended purpose. idx_user_id_id and idx_created_at_type are
unaffected.

Note: GORM AutoMigrate does not change the column order of an already-existing
index with the same name, so existing deployments must rebuild the index
manually (see PR description for per-database DDL).

Co-authored-by: wuyupeng <wuyupeng@floatmiracle.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

model/log.go

@@ -32,9 +32,9 @@ func applyExplicitLogTextFilter(tx *gorm.DB, column string, value string) (*gorm
 }
 
 type Log struct {
-	Id                int    `json:"id" gorm:"index:idx_created_at_id,priority:1;index:idx_user_id_id,priority:2"`
+	Id                int    `json:"id" gorm:"index:idx_created_at_id,priority:2;index:idx_user_id_id,priority:2"`
 	UserId            int    `json:"user_id" gorm:"index;index:idx_user_id_id,priority:1"`
-	CreatedAt         int64  `json:"created_at" gorm:"bigint;index:idx_created_at_id,priority:2;index:idx_created_at_type"`
+	CreatedAt         int64  `json:"created_at" gorm:"bigint;index:idx_created_at_id,priority:1;index:idx_created_at_type"`
 	Type              int    `json:"type" gorm:"index:idx_created_at_type"`
 	Content           string `json:"content"`
 	Username          string `json:"username" gorm:"index;index:index_username_model_name,priority:2;default:''"`