feat: provider api_formats 可空继承、OpenAI 图片 edit/variation 与用量配额多项补强

- 鉴权: provider_api_keys.api_formats 改为可空，OAuth 托管 key 自动继承 provider endpoints 激活格式，相关 handler/测试同步更新
- 图片 planner: OpenAI 图片路由新增 edit/variation 操作并完善参数校验、响应合并与流式处理
- 用量: user me usage 返回区分 client_requested_stream/upstream_is_stream，前端 usage 列表筛选与展示增强
- 统计: stats_daily_model 新增 cache_creation_ephemeral_5m/1h tokens 字段与回填链路
- 配额/observability: quota repository 新增内存与 SQL 扩展，admin observability usage 字段扩充
- 其它: OAuth 导入/轮询收敛、provider 汇总与 pool admin 读写链路小修、新增 system_config 缓存与 provider template handler

Closes #318

Co-authored-by: Entropy.Xu <53283266+Entropy-Xu@users.noreply.github.com>

apps/aether-gateway/src/cache/mod.rs

@@ -3,6 +3,7 @@ mod auth_context;
 mod dashboard_response;
 mod direct_plan_bypass;
 mod scheduler_affinity;
+mod system_config;
 
 pub(crate) use auth_api_key_last_used::AuthApiKeyLastUsedCache;
 pub(crate) use auth_context::AuthContextCache;
@@ -11,3 +12,4 @@ pub(crate) use direct_plan_bypass::DirectPlanBypassCache;
 pub(crate) use scheduler_affinity::{
     SchedulerAffinityCache, SchedulerAffinitySnapshotEntry, SchedulerAffinityTarget,
 };
+pub(crate) use system_config::SystemConfigCache;

apps/aether-gateway/src/cache/system_config.rs

@@ -0,0 +1,32 @@
+use std::time::Duration;
+
+use aether_cache::ExpiringMap;
+
+const MAX_ENTRIES: usize = 512;
+
+#[derive(Debug)]
+pub(crate) struct SystemConfigCache {
+    entries: ExpiringMap<String, Option<serde_json::Value>>,
+}
+
+impl Default for SystemConfigCache {
+    fn default() -> Self {
+        Self {
+            entries: ExpiringMap::new(),
+        }
+    }
+}
+
+impl SystemConfigCache {
+    pub(crate) fn get(&self, key: &str, ttl: Duration) -> Option<Option<serde_json::Value>> {
+        self.entries.get_fresh(&key.to_string(), ttl)
+    }
+
+    pub(crate) fn insert(&self, key: String, value: Option<serde_json::Value>, ttl: Duration) {
+        self.entries.insert(key, value, ttl, MAX_ENTRIES);
+    }
+
+    pub(crate) fn clear(&self) {
+        self.entries.clear();
+    }
+}