refactor: 拆分 gateway 单体为独立 crate，新增 systemd 部署方案

将 gateway 内部的 model-fetch、provider-transport、scheduler-core、
usage-runtime、video-tasks-core 模块提取为独立 crate；重构 gateway
内部模块结构（state/router/cache/data/query 等）；移除大量遗留模块
文件；新增 systemd 二进制部署骨架及相关文档；更新前端 usage 相关
API 和组件。

crates/aether-video-tasks-core/src/follow_up.rs

@@ -0,0 +1,123 @@
+use serde_json::{Map, Value};
+
+pub fn build_video_follow_up_report_context(
+    request_id: &str,
+    user_id: &str,
+    api_key_id: &str,
+    task_id: &str,
+    provider_id: &str,
+    endpoint_id: &str,
+    key_id: &str,
+    provider_name: Option<&str>,
+    model_name: Option<&str>,
+    client_api_format: &str,
+    provider_api_format: &str,
+) -> Value {
+    let mut context = Map::new();
+    context.insert(
+        "request_id".to_string(),
+        Value::String(request_id.to_string()),
+    );
+    context.insert("user_id".to_string(), Value::String(user_id.to_string()));
+    context.insert(
+        "api_key_id".to_string(),
+        Value::String(api_key_id.to_string()),
+    );
+    context.insert("task_id".to_string(), Value::String(task_id.to_string()));
+    context.insert(
+        "provider_id".to_string(),
+        Value::String(provider_id.to_string()),
+    );
+    context.insert(
+        "endpoint_id".to_string(),
+        Value::String(endpoint_id.to_string()),
+    );
+    context.insert("key_id".to_string(), Value::String(key_id.to_string()));
+    context.insert(
+        "client_api_format".to_string(),
+        Value::String(client_api_format.to_string()),
+    );
+    context.insert(
+        "provider_api_format".to_string(),
+        Value::String(provider_api_format.to_string()),
+    );
+    if let Some(provider_name) = provider_name.filter(|value| !value.is_empty()) {
+        context.insert(
+            "provider_name".to_string(),
+            Value::String(provider_name.to_string()),
+        );
+    }
+    if let Some(model_name) = model_name.filter(|value| !value.is_empty()) {
+        context.insert("model".to_string(), Value::String(model_name.to_string()));
+    }
+    Value::Object(context)
+}
+
+pub fn resolve_follow_up_auth(
+    user_id: Option<&str>,
+    api_key_id: Option<&str>,
+    fallback_user_id: Option<&str>,
+    fallback_api_key_id: Option<&str>,
+) -> Option<(String, String)> {
+    let resolved_user_id = user_id
+        .map(str::trim)
+        .filter(|value| !value.is_empty())
+        .map(str::to_string)
+        .or_else(|| {
+            fallback_user_id
+                .map(str::trim)
+                .filter(|value| !value.is_empty())
+                .map(str::to_string)
+        })?;
+    let resolved_api_key_id = api_key_id
+        .map(str::trim)
+        .filter(|value| !value.is_empty())
+        .map(str::to_string)
+        .or_else(|| {
+            fallback_api_key_id
+                .map(str::trim)
+                .filter(|value| !value.is_empty())
+                .map(str::to_string)
+        })?;
+    Some((resolved_user_id, resolved_api_key_id))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{build_video_follow_up_report_context, resolve_follow_up_auth};
+
+    #[test]
+    fn builds_follow_up_report_context_with_transport_metadata() {
+        let context = build_video_follow_up_report_context(
+            "req_123",
+            "user_123",
+            "key_123",
+            "task_123",
+            "provider_123",
+            "endpoint_123",
+            "transport_key_123",
+            Some("provider-name"),
+            Some("model-name"),
+            "openai:video",
+            "openai:video",
+        );
+
+        assert_eq!(context["request_id"].as_str(), Some("req_123"));
+        assert_eq!(context["provider_id"].as_str(), Some("provider_123"));
+        assert_eq!(context["provider_name"].as_str(), Some("provider-name"));
+        assert_eq!(context["model"].as_str(), Some("model-name"));
+    }
+
+    #[test]
+    fn resolves_follow_up_auth_from_primary_or_fallback_values() {
+        assert_eq!(
+            resolve_follow_up_auth(Some(" user_123 "), Some(" key_123 "), None, None),
+            Some(("user_123".to_string(), "key_123".to_string()))
+        );
+        assert_eq!(
+            resolve_follow_up_auth(None, None, Some("user_fallback"), Some("key_fallback")),
+            Some(("user_fallback".to_string(), "key_fallback".to_string()))
+        );
+        assert_eq!(resolve_follow_up_auth(None, None, None, None), None);
+    }
+}