refactor: 移除 Python upstream 依赖，清理全部 legacy/Python 兼容层

- 移除 upstream_base_url 参数及 AETHER_GATEWAY_UPSTREAM 环境变量，gateway 不再需要指向 Python 宿主
- 删除所有 LEGACY_*/PYTHON_* 常量、路由组、header 定义及 sunset/phaseout 机制
- 将 legacy_gateway_bridge 重命名为 internal_gateway，executor 相关命名统一为 execution_runtime
- dev.sh 新增 Postgres/Redis 预检查，移除 upstream 相关启动参数和提示
- 新增 ai_public 路由处理器
- 全量适配 handler、test、state、control 等模块的命名和接口变更

apps/aether-gateway/src/ai_pipeline/adaptation/kiro_stream/stream/tests.rs

@@ -1,7 +1,8 @@
 use super::util::crc32;
-use super::*;
 use serde_json::{json, Value};
 
+use super::KiroToClaudeCliStreamState;
+
 fn encode_string_header(name: &str, value: &str) -> Vec<u8> {
     let mut out = Vec::new();
     out.push(name.len() as u8);

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

@@ -139,7 +139,14 @@ pub(crate) fn provider_adaptation_should_unwrap_stream_envelope(
 
 #[cfg(test)]
 mod tests {
-    use super::*;
+    use super::{
+        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,
+    };
 
     #[test]
     fn resolves_private_surface_anchor_contracts() {