feat(ai): 新增预算状态 + 成本估算 API 端点

Phase 3 Task 25:
- GET /ai/budget/status — 租户月度预算状态和告警等级
- GET /ai/cost/estimate — 按分析类型+模型估算单次成本

crates/erp-ai/src/handler/mod.rs

@@ -558,6 +558,42 @@ where
     Ok(Json(ApiResponse::ok(result)))
 }
 
+// === 成本与预算 ===
+
+pub async fn budget_status<S>(
+    State(state): State<AiState>,
+    Extension(ctx): Extension<TenantContext>,
+) -> Result<Json<ApiResponse<crate::service::cost::BudgetStatus>>, erp_core::error::AppError>
+where
+    AiState: FromRef<S>,
+    S: Clone + Send + Sync + 'static,
+{
+    require_permission(&ctx, "ai.usage.list")?;
+    let cost_svc = crate::service::cost::CostService::new(state.db.clone());
+    let status = cost_svc.get_budget_status(ctx.tenant_id).await?;
+    Ok(Json(ApiResponse::ok(status)))
+}
+
+#[derive(Debug, Deserialize)]
+pub struct CostEstimateQuery {
+    pub analysis_type: String,
+    pub model: Option<String>,
+}
+
+pub async fn cost_estimate<S>(
+    Extension(ctx): Extension<TenantContext>,
+    Query(params): Query<CostEstimateQuery>,
+) -> Result<Json<ApiResponse<crate::service::cost::CostEstimate>>, erp_core::error::AppError>
+where
+    AiState: FromRef<S>,
+    S: Clone + Send + Sync + 'static,
+{
+    require_permission(&ctx, "ai.usage.list")?;
+    let model = params.model.unwrap_or_else(|| "claude-sonnet-4-6".to_string());
+    let estimate = crate::service::cost::CostService::estimate_cost(&params.analysis_type, &model);
+    Ok(Json(ApiResponse::ok(estimate)))
+}
+
 // === SSE 流构建辅助 ===
 
 fn build_sse_stream(

crates/erp-ai/src/module.rs

@@ -359,5 +359,13 @@ impl AiModule {
                 "/ai/quota/summary",
                 axum::routing::get(crate::handler::quota_summary),
             )
+            .route(
+                "/ai/budget/status",
+                axum::routing::get(crate::handler::budget_status),
+            )
+            .route(
+                "/ai/cost/estimate",
+                axum::routing::get(crate::handler::cost_estimate),
+            )
     }
 }