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。

apps/aether-gateway/src/ai_pipeline/adaptation/kiro/mod.rs

@@ -64,13 +64,13 @@ enum FrameParseError {
     Invalid(String),
 }
 
-#[path = "kiro_stream/stream/decoder.rs"]
+#[path = "stream/decoder.rs"]
 mod decoder;
-#[path = "kiro_stream/stream/state.rs"]
+#[path = "stream/state.rs"]
 mod state;
-#[path = "kiro_stream/stream/util.rs"]
+#[path = "stream/util.rs"]
 mod util;
 
 #[cfg(test)]
-#[path = "kiro_stream/stream/tests.rs"]
+#[path = "stream/tests.rs"]
 mod tests;

apps/aether-gateway/src/ai_pipeline/adaptation/kiro/stream/state.rs

@@ -1,7 +1,7 @@
 use serde_json::{json, Value};
 use uuid::Uuid;
 
-use crate::gateway::GatewayError;
+use crate::GatewayError;
 
 use super::util::{
     encode_events, estimate_tokens, find_real_thinking_end_tag,

apps/aether-gateway/src/ai_pipeline/adaptation/kiro/stream/util.rs

@@ -1,6 +1,6 @@
 use serde_json::Value;
 
-use crate::gateway::GatewayError;
+use crate::GatewayError;
 
 use super::QUOTE_CHARS;
 

apps/aether-gateway/src/ai_pipeline/adaptation/mod.rs

@@ -1,8 +1,8 @@
-pub(crate) mod kiro_stream;
+pub(crate) mod kiro;
 pub(crate) mod private_envelope;
 pub(crate) mod surfaces;
 
-pub(crate) use kiro_stream::KiroToClaudeCliStreamState;
+pub(crate) use kiro::KiroToClaudeCliStreamState;
 pub(crate) use private_envelope::{
     maybe_build_provider_private_stream_normalizer,
     maybe_normalize_provider_private_sync_report_payload,

apps/aether-gateway/src/ai_pipeline/adaptation/private_envelope.rs

@@ -3,13 +3,15 @@ use std::collections::BTreeMap;
 use base64::Engine as _;
 use serde_json::Value;
 
-use crate::gateway::ai_pipeline::adaptation::surfaces::{
+use crate::ai_pipeline::adaptation::surfaces::{
     provider_adaptation_allows_sync_finalize_envelope, provider_adaptation_descriptor_for_envelope,
     provider_adaptation_should_unwrap_stream_envelope, ANTIGRAVITY_V1INTERNAL_ENVELOPE_NAME,
     GEMINI_CLI_V1INTERNAL_ENVELOPE_NAME,
 };
-use crate::gateway::ai_pipeline::runtime::{KiroToClaudeCliStreamState, KIRO_ENVELOPE_NAME};
-use crate::gateway::{GatewayError, GatewaySyncReportRequest};
+use crate::ai_pipeline::runtime::adapters::kiro::{
+    KiroToClaudeCliStreamState, KIRO_ENVELOPE_NAME,
+};
+use crate::{usage::GatewaySyncReportRequest, GatewayError};
 
 enum ProviderPrivateStreamNormalizeMode {
     EnvelopeUnwrap,

apps/aether-gateway/src/ai_pipeline/adaptation/surfaces.rs

@@ -1,4 +1,4 @@
-use crate::gateway::ai_pipeline::runtime::adapters::{
+use crate::ai_pipeline::runtime::adapters::{
     antigravity::ANTIGRAVITY_PROVIDER_TYPE,
     kiro::{KIRO_ENVELOPE_NAME, PROVIDER_TYPE as KIRO_PROVIDER_TYPE},
 };
@@ -140,12 +140,10 @@ pub(crate) fn provider_adaptation_should_unwrap_stream_envelope(
 #[cfg(test)]
 mod tests {
     use super::{
-        provider_adaptation_allows_sync_finalize_envelope,
-        provider_adaptation_anchor_api_format,
+        provider_adaptation_allows_sync_finalize_envelope, provider_adaptation_anchor_api_format,
         provider_adaptation_requires_eventstream_accept,
-        provider_adaptation_should_unwrap_stream_envelope,
-        ANTIGRAVITY_V1INTERNAL_ENVELOPE_NAME, GEMINI_CLI_V1INTERNAL_ENVELOPE_NAME,
-        KIRO_ENVELOPE_NAME,
+        provider_adaptation_should_unwrap_stream_envelope, ANTIGRAVITY_V1INTERNAL_ENVELOPE_NAME,
+        GEMINI_CLI_V1INTERNAL_ENVELOPE_NAME, KIRO_ENVELOPE_NAME,
     };
 
     #[test]