Add LICENSE, AGENTS.md, and richer package metadata

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: 2 people

AGENTS.md

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+# AGENTS.md — uapi-sdk-cpp
+
+This file tells AI coding agents how to use the **official C++ SDK** for
+the [uapis.cn](https://uapis.cn) public API platform.
+
+## What this library is
+
+Header-only C++17 client for UAPI. Generated from the live OpenAPI 3.1
+spec at <https://uapis.cn/openapi.json>.
+
+## Install
+
+CMake (FetchContent):
+
+```cmake
+include(FetchContent)
+FetchContent_Declare(
+  uapi-sdk-cpp
+  GIT_REPOSITORY https://github.com/AxT-Team/uapi-sdk-cpp
+  GIT_TAG main
+)
+FetchContent_MakeAvailable(uapi-sdk-cpp)
+
+target_link_libraries(my_app PRIVATE uapi)
+```
+
+## Quick start
+
+```cpp
+#include <uapi/client.hpp>
+
+int main() {
+    uapi::Client client("https://uapis.cn");
+
+    auto weather = client.misc().get_misc_weather({.city = "北京"});
+    std::cout << weather.dump() << std::endl;
+}
+```
+
+The client is grouped by tag (`misc()`, `network()`, `text()`, `image()`,
+`social()`, `translate()`, `search()`, …). Method names match the OpenAPI
+`operationId`, snake_cased.
+
+## Authentication
+
+Free-tier endpoints work with no key. Paid endpoints take a key:
+
+```cpp
+uapi::Client client("https://uapis.cn", "sk_…");
+```
+
+## Errors
+
+Methods throw `uapi::ApiException` on non-2xx responses. The exception
+carries `code`, `error`, and `request_id` fields. Surface `error`
+verbatim.
+
+## Rate limits
+
+Headers `X-RateLimit-Limit`, `X-RateLimit-Remaining`, `X-RateLimit-Reset`,
+`Retry-After` are exposed on response headers. Honor them.
+
+## Related repos
+
+- MCP server: <https://github.com/AxT-Team/uapi-mcp>.
+- Skills bundle: <https://github.com/AxT-Team/uapi-agent-skills>.
+- Other languages: `uapi-sdk-typescript`, `uapi-sdk-python`, `uapi-sdk-go`,
+  `uapi-sdk-rust`, `uapi-sdk-java`, `uapi-sdk-csharp`, `uapi-sdk-php`.

LICENSE

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+MIT License
+
+Copyright (c) 2025 AxT-Team / UAPI
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.