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

apps/aether-gateway/src/data/state/integrations.rs

@@ -157,6 +157,21 @@ impl MinimalCandidateSelectionRowSource for GatewayDataState {
 
 #[async_trait]
 impl BillingModelContextLookup for GatewayDataState {
+    async fn find_billing_model_context_by_model_id(
+        &self,
+        provider_id: &str,
+        provider_api_key_id: Option<&str>,
+        model_id: &str,
+    ) -> Result<Option<StoredBillingModelContext>, DataLayerError> {
+        GatewayDataState::find_billing_model_context_by_model_id(
+            self,
+            provider_id,
+            provider_api_key_id,
+            model_id,
+        )
+        .await
+    }
+
     async fn find_billing_model_context(
         &self,
         provider_id: &str,

apps/aether-gateway/src/data/state/runtime.rs

@@ -1241,6 +1241,22 @@ impl GatewayDataState {
         }
     }
 
+    pub(crate) async fn find_billing_model_context_by_model_id(
+        &self,
+        provider_id: &str,
+        provider_api_key_id: Option<&str>,
+        model_id: &str,
+    ) -> Result<Option<StoredBillingModelContext>, DataLayerError> {
+        match &self.billing_reader {
+            Some(repository) => {
+                repository
+                    .find_model_context_by_model_id(provider_id, provider_api_key_id, model_id)
+                    .await
+            }
+            None => Ok(None),
+        }
+    }
+
     pub(crate) async fn read_request_candidate_trace(
         &self,
         request_id: &str,