refactor: 大规模模块拆分与代码精简，新增 ai-pipeline/data-contracts 独立 crate

- 新增 aether-ai-pipeline 和 aether-data-contracts crate，将 pipeline 逻辑与数据契约从 gateway 中解耦
- 重构 admin handlers：拆分单体模块为 auth/billing/endpoint/features/model/observability/provider/system 等独立子模块
- 合并 chat/cli 重复代码路径：精简 conversion、finalize、planner 中的 sync/chat/cli 分支
- 重构 scheduler/executor/data 层，引入 facade 模式降低模块间耦合
- 移除冗余的 intent 模块，将 plan_fallback/policy/stream_path/sync_path 迁移至 executor
- 前端适配：调整 admin API 调用和 provider 模型测试对话框

crates/aether-data-contracts/src/repository/quota/mod.rs

@@ -0,0 +1,6 @@
+mod types;
+
+pub use types::{
+    ProviderQuotaReadRepository, ProviderQuotaRepository, ProviderQuotaWriteRepository,
+    StoredProviderQuotaSnapshot,
+};

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

@@ -0,0 +1,71 @@
+use async_trait::async_trait;
+
+#[derive(Debug, Clone, PartialEq, serde::Serialize, serde::Deserialize)]
+pub struct StoredProviderQuotaSnapshot {
+    pub provider_id: String,
+    pub billing_type: String,
+    pub monthly_quota_usd: Option<f64>,
+    pub monthly_used_usd: f64,
+    pub quota_reset_day: Option<u64>,
+    pub quota_last_reset_at_unix_secs: Option<u64>,
+    pub quota_expires_at_unix_secs: Option<u64>,
+    pub is_active: bool,
+}
+
+impl StoredProviderQuotaSnapshot {
+    #[allow(clippy::too_many_arguments)]
+    pub fn new(
+        provider_id: String,
+        billing_type: String,
+        monthly_quota_usd: Option<f64>,
+        monthly_used_usd: f64,
+        quota_reset_day: Option<i32>,
+        quota_last_reset_at_unix_secs: Option<i64>,
+        quota_expires_at_unix_secs: Option<i64>,
+        is_active: bool,
+    ) -> Result<Self, crate::DataLayerError> {
+        if provider_id.trim().is_empty() || billing_type.trim().is_empty() {
+            return Err(crate::DataLayerError::UnexpectedValue(
+                "provider quota identity is empty".to_string(),
+            ));
+        }
+        if !monthly_used_usd.is_finite() || monthly_quota_usd.is_some_and(|v| !v.is_finite()) {
+            return Err(crate::DataLayerError::UnexpectedValue(
+                "provider quota value is not finite".to_string(),
+            ));
+        }
+        Ok(Self {
+            provider_id,
+            billing_type,
+            monthly_quota_usd,
+            monthly_used_usd,
+            quota_reset_day: quota_reset_day.map(|value| value as u64),
+            quota_last_reset_at_unix_secs: quota_last_reset_at_unix_secs.map(|value| value as u64),
+            quota_expires_at_unix_secs: quota_expires_at_unix_secs.map(|value| value as u64),
+            is_active,
+        })
+    }
+}
+
+#[async_trait]
+pub trait ProviderQuotaReadRepository: Send + Sync {
+    async fn find_by_provider_id(
+        &self,
+        provider_id: &str,
+    ) -> Result<Option<StoredProviderQuotaSnapshot>, crate::DataLayerError>;
+}
+
+#[async_trait]
+pub trait ProviderQuotaWriteRepository: Send + Sync {
+    async fn reset_due(&self, now_unix_secs: u64) -> Result<usize, crate::DataLayerError>;
+}
+
+pub trait ProviderQuotaRepository:
+    ProviderQuotaReadRepository + ProviderQuotaWriteRepository + Send + Sync
+{
+}
+
+impl<T> ProviderQuotaRepository for T where
+    T: ProviderQuotaReadRepository + ProviderQuotaWriteRepository + Send + Sync
+{
+}