feat: 扩展 Rust gateway 全功能模块，新增 billing/crypto/wallet crate 及完整数据层

- 新增 aether-billing、aether-crypto、aether-wallet 独立 crate
- aether-data 扩展 repository 层：announcements、auth_modules、billing、
  candidate_selection、gemini_file_mappings、global_models、management_tokens、
  oauth_providers、proxy_nodes、quota、users、wallet 等模块
- aether-gateway 新增 api/auth/billing/control/middleware/scheduler/usage/
  video_tasks/hooks/maintenance/model_fetch/provider_transport 等功能模块
- 重构 executor decision 和 gateway state 为模块目录结构
- 新增 gateway router、frontdoor 路由层及对应测试
- Python 侧 API 路由重构，新增 compat/support 模块
- 前端 Logo 组件更新及 Provider 管理页面调整

crates/aether-billing/src/precision.rs

@@ -0,0 +1,33 @@
+pub const BILLING_STORAGE_PRECISION: u32 = 8;
+pub const BILLING_DISPLAY_PRECISION: u32 = 6;
+
+pub fn quantize_value(value: f64, precision: u32) -> f64 {
+    if !value.is_finite() {
+        return value;
+    }
+    let factor = 10_f64.powi(precision as i32);
+    (value * factor).round() / factor
+}
+
+pub fn quantize_cost(value: f64) -> f64 {
+    quantize_value(value, BILLING_STORAGE_PRECISION)
+}
+
+pub fn quantize_display(value: f64) -> f64 {
+    quantize_value(value, BILLING_DISPLAY_PRECISION)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{quantize_cost, quantize_display};
+
+    #[test]
+    fn quantizes_cost_to_storage_precision() {
+        assert_eq!(quantize_cost(1.234567891), 1.23456789);
+    }
+
+    #[test]
+    fn quantizes_display_to_display_precision() {
+        assert_eq!(quantize_display(1.23456789), 1.234568);
+    }
+}