refactor: 移除 Python 后端源码，全面迁移至 Rust gateway 架构

- 删除全部 Python 源码 (src/) 及 Alembic 迁移脚本，归档至 _deprecated_py_src/
- 重构 Rust gateway ai_pipeline: 拆分 planner/finalize 模块，新增 contracts/adaptation 层
- 重组 handlers 模块为 admin/public/proxy/internal/shared 子模块结构
- 新增 executor 模块，引入 Rust 原生数据库迁移 (aether-data/migrations)
- 简化 CI/Docker 构建流程，移除 base image 二级构建，统一为单一 app image
- 移除 Python 相关基础设施文件 (entrypoint.sh, gunicorn_conf.py, Dockerfile.base)

apps/aether-gateway/src/handlers/admin/mod.rs

@@ -0,0 +1,74 @@
+pub(crate) use super::*;
+
+mod adaptive;
+mod api_keys;
+mod billing;
+mod catalog_write_helpers;
+mod core;
+mod endpoints;
+mod endpoints_health_helpers;
+mod gemini_files;
+mod global_models;
+mod ldap;
+mod misc_helpers;
+mod models_helpers;
+mod monitoring;
+mod oauth_helpers;
+mod payments;
+mod pool;
+mod provider_models;
+#[path = "provider_oauth/dispatch.rs"]
+mod provider_oauth_dispatch;
+#[path = "provider_oauth/quota.rs"]
+mod provider_oauth_quota;
+#[path = "provider_oauth/refresh.rs"]
+mod provider_oauth_refresh;
+#[path = "provider_oauth/state.rs"]
+mod provider_oauth_state;
+mod provider_ops;
+mod provider_query;
+mod provider_strategy;
+mod providers;
+mod providers_helpers;
+mod proxy_nodes;
+mod security;
+mod stats;
+mod usage;
+mod users;
+mod video_tasks;
+mod wallets;
+
+pub(crate) use self::adaptive::*;
+pub(crate) use self::api_keys::*;
+pub(crate) use self::billing::*;
+pub(crate) use self::catalog_write_helpers::*;
+pub(crate) use self::core::*;
+pub(crate) use self::endpoints::*;
+pub(crate) use self::endpoints_health_helpers::*;
+pub(crate) use self::gemini_files::*;
+pub(crate) use self::global_models::*;
+pub(crate) use self::ldap::*;
+pub(crate) use self::misc_helpers::*;
+pub(crate) use self::models_helpers::*;
+pub(crate) use self::monitoring::maybe_build_local_admin_monitoring_root_response as maybe_build_local_admin_monitoring_response;
+pub(crate) use self::oauth_helpers::*;
+pub(crate) use self::payments::*;
+pub(crate) use self::pool::*;
+pub(crate) use self::provider_models::*;
+pub(crate) use self::provider_oauth_dispatch::*;
+pub(crate) use self::provider_oauth_quota::*;
+pub(crate) use self::provider_oauth_refresh::*;
+pub(crate) use self::provider_oauth_state::*;
+pub(crate) use self::provider_ops::admin_provider_ops_local_action_response;
+pub(crate) use self::provider_ops::maybe_build_local_admin_provider_ops_response;
+pub(crate) use self::provider_query::*;
+pub(crate) use self::provider_strategy::*;
+pub(crate) use self::providers::*;
+pub(crate) use self::providers_helpers::*;
+pub(crate) use self::proxy_nodes::*;
+pub(crate) use self::security::*;
+pub(crate) use self::stats::*;
+pub(crate) use self::usage::*;
+pub(crate) use self::users::*;
+pub(crate) use self::video_tasks::*;
+pub(crate) use self::wallets::*;