feat: show normalized prompt cache hit rates

Token usage previously showed cache reads and writes without a comparable hit rate. Activity usage now calculates a weighted cache hit rate using OpenAI-compatible input totals and Anthropic's separately reported input, cache-read, and cache-write tokens, then shows it in totals and grouped details.

Release note: Token 用量统计新增缓存命中率，并针对 OpenAI 兼容接口与 Anthropic Messages 的不同上报口径进行归一化计算。

src/shared/assistant-contracts.ts

@@ -379,6 +379,7 @@ export type TokenUsageRecord = {
   output: number
   cacheRead: number
   cacheWrite: number
+  cacheInput?: number
   totalTokens: number
 }
 
@@ -389,6 +390,7 @@ export type TokenUsageSummary = {
     output: number
     cacheRead: number
     cacheWrite: number
+    cacheInput?: number
     totalTokens: number
   }
   records: TokenUsageRecord[]