feat(billing): 引入 model_id 精确计费查找路径，传播模型 ID 至用量事件与 report context

- UsageEventData 新增 model_id / global_model_id 字段，write.rs seed 结构体同步补充
- report_context 新增 model_id / global_model_id / global_model_name，各 payload 构建时从 candidate 传入
- event_enrichment 优先按 model_id 精确查找计费上下文，回退为按名称多轮查找（保留 NoRule 结果降级逻辑）
- BillingReadRepository 新增 find_model_context_by_model_id，memory/sql 分别实现；SQL 查询重构支持按 provider_model_name 和 mappings 匹配并按优先级排序
- pricing.rs 修复：model_tiered_pricing 为空 tiers 时回退到 default_tiered_pricing
- request_metadata 允许字段列表补充 model_id / global_model_id / global_model_name
- admin usage 路由信息输出及脱敏字段列表同步新增三个 model 相关字段

crates/aether-data-contracts/src/repository/billing/types.rs

@@ -150,4 +150,14 @@ pub trait BillingReadRepository: Send + Sync {
         provider_api_key_id: Option<&str>,
         global_model_name: &str,
     ) -> Result<Option<StoredBillingModelContext>, crate::DataLayerError>;
+
+    async fn find_model_context_by_model_id(
+        &self,
+        provider_id: &str,
+        provider_api_key_id: Option<&str>,
+        model_id: &str,
+    ) -> Result<Option<StoredBillingModelContext>, crate::DataLayerError> {
+        let _ = (provider_id, provider_api_key_id, model_id);
+        Ok(None)
+    }
 }

crates/aether-data-contracts/src/repository/usage/types.rs

@@ -500,6 +500,18 @@ impl StoredRequestUsageAudit {
             .or_else(|| self.request_metadata_string("key_name"))
     }
 
+    pub fn routing_model_id(&self) -> Option<&str> {
+        self.request_metadata_string("model_id")
+    }
+
+    pub fn routing_global_model_id(&self) -> Option<&str> {
+        self.request_metadata_string("global_model_id")
+    }
+
+    pub fn routing_global_model_name(&self) -> Option<&str> {
+        self.request_metadata_string("global_model_name")
+    }
+
     pub fn routing_planner_kind(&self) -> Option<&str> {
         self.planner_kind
             .as_deref()