feat(cw): archive decoded history, polish the waterfall, document licensing

三个用户反馈一并解决:

1. 解码文字不再消失 (核心)
   旧实现: 20 秒环形缓冲满了就静默覆盖最旧样本, 文字随之从屏幕消失。
   新实现: CwDeepBuffer 新增 overflow —— 满时被覆盖的旧样本先进 overflow,
   解码器累积到 15 秒就单独解码一次, 结果追加到 historyText (只增不减)。
   UI 记录区显示 historyText + decodedText (历史稳定 + 当前窗口实时)。
   ICwDecoder 接口新增 historyText StateFlow。

   归档音频已离开主窗口, 不再被 CTC 修正, 故其文本是"最终版", 追加安全。
   归档窗口 15 秒: 内容已在 20 秒窗口里解过多次, 短一点几乎无损, 且推理
   开销小。

2. 瀑布图更好看
   配色从"深蓝->青->黄"换成 matplotlib inferno (黑->紫->品红->橙->黄),
   与静态频谱图保持一致。相邻 bin 之间用水平渐变做线性插值, 消除 65 列
   离散方块的像素感。

3. AGPL 合规补漏 (用户提醒: 仓库许可证没体现 AGPL 组件)
   README 新增 License 章节: 声明项目主体 GPL-3.0 + feature/cw 的 DeepCW
   模型 AGPL-3.0-only, 并说明合并作品按 GPL-3.0 §13 / AGPL-3.0 §13 处理。

验证:
- :core:domain:test => 31 个 CW 测试全绿 (CwDeepBufferTest 新增 3 个
  overflow 归档测试: 顺序/清空/reset)
- :core:domain:compileKotlin + :core:data + :feature:cw:compileDebugKotlin
  => BUILD SUCCESSFUL

README.md

@@ -34,6 +34,21 @@ It is now and always will be completely ad-free and open-source.
 *  Custom TLE satellite data import is available via Three Line Element .txt files
 *  Offline first: calculations are made offline. Weekly TLE data update is recommended.
 
+## License
+
+Look4Sat is free software licensed under the [GNU General Public License v3.0](LICENSE).
+
+The CW decoder in `feature/cw` bundles the [DeepCW](https://github.com/e04/deepcw-engine)
+neural decoding model, which is licensed under the
+[GNU Affero General Public License v3.0](feature/cw/licenses/DeepCW-AGPL-3.0.txt)
+(AGPL-3.0-only). Provenance, attribution and the applied int8 quantization are
+documented in [`feature/cw/licenses/NOTICE.md`](feature/cw/licenses/NOTICE.md).
+
+Because the combined work incorporates an AGPL-3.0 component, the requirements of
+AGPL-3.0 Section 13 apply to the combined work as a whole when it is distributed
+(GPL-3.0 Section 13 permits this combination). The CW model runs locally on-device
+and does not provide services over a network.
+
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