feat: add real-time caption CLI prototype with Qwen3-ASR

Add a C++/Qt6/CMake CLI prototype that captures the default sink
monitor through libpulse and transcribes it in-process with Qwen3-ASR
via libllama/libmtmd. Add phase 0/1 verification docs.

新增实时字幕命令行原型：libpulse 采集默认输出 monitor，进程内用
libllama/libmtmd 跑 Qwen3-ASR 推理。附阶段 0/1 验证文档。

.gitignore

@@ -0,0 +1,7 @@
+# build 产物与本地模型
+/build/
+/models/
+
+# 编辑器
+.cache/
+compile_commands.json