feat(stats,rules): api_key 用量统计（total_tokens 字段 + 回填）与 body rules 新增 append/insert/regex_replace/name_style 操作

- 新增迁移 20260422120000_add_api_key_usage_stats.sql，为 api_keys 表添加 total_tokens 列
- 新增回填 20260422120000_backfill_api_key_usage_stats.sql，按历史 usage 重建 api_key 维度汇总
- 在 UsageWriteRepository trait 中添加 rebuild_api_key_usage_stats，补齐 SQL/内存实现及上层调用链
- 内存实现中新增 apply_usage_stats_delta，支持增量更新 api_key 统计快照
- dev.sh：改进临时日志目录管理，并在网关异常退出时输出错误提示
- frontend EndpointFormDialog：将 append 操作从 insert 分支拆分，提供独立 path/value 输入 UI
- rules.rs：扩展 body rules 支持，新增 append/insert/regex_replace/name_style 操作及 WildcardSlice 路径段

crates/aether-data/backfills/20260422120000_backfill_api_key_usage_stats.sql

@@ -0,0 +1,38 @@
+UPDATE public.api_keys
+SET
+    total_requests = 0,
+    total_tokens = 0,
+    total_cost_usd = 0,
+    last_used_at = NULL;
+
+WITH aggregated AS (
+    SELECT
+        usage.api_key_id,
+        COUNT(*)::INTEGER AS total_requests,
+        COALESCE(
+            SUM(
+                GREATEST(
+                    COALESCE(
+                        usage.total_tokens,
+                        COALESCE(usage.input_tokens, 0) + COALESCE(usage.output_tokens, 0)
+                    ),
+                    0
+                )::BIGINT
+            ),
+            0
+        )::BIGINT AS total_tokens,
+        COALESCE(SUM(COALESCE(usage.total_cost_usd, 0)), 0)::NUMERIC(20,8) AS total_cost_usd,
+        MAX(usage.created_at) AS last_used_at
+    FROM public.usage
+    WHERE usage.api_key_id IS NOT NULL
+      AND BTRIM(usage.api_key_id) <> ''
+    GROUP BY usage.api_key_id
+)
+UPDATE public.api_keys
+SET
+    total_requests = aggregated.total_requests,
+    total_tokens = aggregated.total_tokens,
+    total_cost_usd = aggregated.total_cost_usd,
+    last_used_at = aggregated.last_used_at
+FROM aggregated
+WHERE public.api_keys.id = aggregated.api_key_id;