feat(stats): 新增聚合读路径与回填机制并重构 dashboard/usage 读取链路

- 新增 stats_user_summary 及 user_daily_provider/api_format/cost_savings 等聚合表
- 扩展 stats_daily/hourly 有效 token 与响应时间等字段，maintenance runtime 同步写入
- 新增 backfill 模块与 --apply-backfills 命令补齐历史聚合数据
- 重写 dashboard_filters、usage_heatmap、user_rollups 查询改走聚合表
- 同步更新 baseline_v2.sql 与 migration 集，README/dev.sh 补充回填用法

apps/aether-gateway/src/tests/control/admin/system_import.rs

@@ -607,6 +607,7 @@ async fn gateway_imports_admin_system_users_locally_and_persists_data() {
                     "expires_at": "2099-01-01T00:00:00Z",
                     "auto_delete_on_expiry": false,
                     "total_requests": 12,
+                    "total_tokens": 3456,
                     "total_cost_usd": 1.25
                 }]
             }],
@@ -622,6 +623,7 @@ async fn gateway_imports_admin_system_users_locally_and_persists_data() {
                 "expires_at": "2099-02-01T00:00:00Z",
                 "auto_delete_on_expiry": false,
                 "total_requests": 3,
+                "total_tokens": 789,
                 "total_cost_usd": 0.75,
                 "wallet": {
                     "balance": 30.0,
@@ -704,6 +706,7 @@ async fn gateway_imports_admin_system_users_locally_and_persists_data() {
         .expect("user api keys should load");
     assert_eq!(user_api_keys.len(), 1);
     assert_eq!(user_api_keys[0].name.as_deref(), Some("Alice CLI"));
+    assert_eq!(user_api_keys[0].total_tokens, 3456);
     assert_eq!(
         user_api_keys[0].allowed_api_formats,
         Some(vec!["openai:chat".to_string()])
@@ -729,6 +732,7 @@ async fn gateway_imports_admin_system_users_locally_and_persists_data() {
         standalone_keys[0].name.as_deref(),
         Some("Imported Standalone")
     );
+    assert_eq!(standalone_keys[0].total_tokens, 789);
     assert_eq!(
         decrypt_python_fernet_ciphertext(
             DEVELOPMENT_ENCRYPTION_KEY,