feat: add output/input ratio column to aggregation page

Add a sortable "Out/In Ratio" (completion_tokens / prompt_tokens)
column with a portal-based tooltip explaining the metric. Fix
hydration mismatch by switching to useSyncExternalStore for
localStorage reads in TimeRangeProvider. Update CLAUDE.md with
project documentation.

lib/i18n.tsx

@@ -68,6 +68,8 @@ const translations = {
     "agg.userCount": "用户数",
     "agg.totalCalls": "总调用",
     "agg.totalToken": "总 Token",
+    "agg.ratio": "转换率",
+    "agg.ratioTip": "输出Token / 输入Token，反映每次请求的生成效率。>1 表示输出多于输入（如生成、写作），<1 表示输入多于输出（如分析、摘要）",
     // logs
     "logs.title": "日志明细",
     "logs.filterUser": "用户名",
@@ -148,6 +150,8 @@ const translations = {
     "agg.userCount": "Users",
     "agg.totalCalls": "Total Calls",
     "agg.totalToken": "Total Token",
+    "agg.ratio": "Out/In Ratio",
+    "agg.ratioTip": "Completion tokens / Prompt tokens. >1 means more output than input (generation, writing); <1 means more input than output (analysis, summarization)",
     "logs.title": "Log Details",
     "logs.filterUser": "Username",
     "logs.filterModel": "Model",