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。

CMakeLists.txt

@@ -0,0 +1,84 @@
+cmake_minimum_required(VERSION 3.24)
+project(live-caption LANGUAGES CXX)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+if(NOT CMAKE_BUILD_TYPE)
+    set(CMAKE_BUILD_TYPE Release CACHE STRING "" FORCE)
+endif()
+
+# ---------------------------------------------------------------------------
+# llama.cpp / libmtmd 的搜索路径
+#
+# Debian/Deepin 把 llama 的 CMake config 放在非标准目录 cmake-private/，
+# 而 pkg-config 的 llama.pc 又漏了 -lmtmd。所以这里把两个路径都塞进搜索前缀，
+# 并单独用 find_library 找 mtmd。
+# ---------------------------------------------------------------------------
+foreach(_p
+        /usr/lib/x86_64-linux-gnu/llama
+        /usr/lib/x86_64-linux-gnu/llama/cmake-private
+        /usr/lib/x86_64-linux-gnu/llama/pkgconfig)
+    if(EXISTS "${_p}")
+        list(APPEND CMAKE_PREFIX_PATH "${_p}")
+        set(ENV{PKG_CONFIG_PATH} "${_p}:$ENV{PKG_CONFIG_PATH}")
+    endif()
+endforeach()
+
+find_package(Qt6 REQUIRED COMPONENTS Core)
+find_package(PkgConfig REQUIRED)
+find_package(Threads REQUIRED)
+
+pkg_check_modules(SAMPLERATE REQUIRED IMPORTED_TARGET samplerate)
+pkg_check_modules(PULSE      REQUIRED IMPORTED_TARGET libpulse)
+
+# --- llama：优先系统 pkg-config，其次 CMake config，最后 FetchContent 兜底 ---
+pkg_check_modules(LLAMA QUIET IMPORTED_TARGET llama)
+if(LLAMA_FOUND)
+    set(LC_LLAMA_TARGET PkgConfig::LLAMA)
+    message(STATUS "llama: 使用系统 pkg-config (${LLAMA_VERSION})")
+else()
+    message(STATUS "llama: 系统未找到，改用 FetchContent 拉取固定版本")
+    include(FetchContent)
+    set(FETCHCONTENT_TRY_FIND_PACKAGE_MODE ALWAYS)   # 先 find_package，失败再拉源码
+    FetchContent_Declare(llama
+        GIT_REPOSITORY https://github.com/ggml-org/llama.cpp.git
+        GIT_TAG        b9951
+        FIND_PACKAGE_ARGS NAMES llama CONFIG)
+    set(LLAMA_BUILD_TESTS  OFF CACHE BOOL "" FORCE)
+    set(LLAMA_BUILD_SERVER OFF CACHE BOOL "" FORCE)
+    set(LLAMA_BUILD_EXAMPLES OFF CACHE BOOL "" FORCE)
+    FetchContent_MakeAvailable(llama)
+    set(LC_LLAMA_TARGET llama)
+endif()
+
+# --- mtmd：llama.pc 里没有，单独找 ---
+find_library(LC_MTMD_LIB NAMES mtmd
+             HINTS /usr/lib/x86_64-linux-gnu/llama)
+if(NOT LC_MTMD_LIB)
+    message(FATAL_ERROR "找不到 libmtmd（应随 libllama0 一起安装）")
+endif()
+message(STATUS "mtmd: ${LC_MTMD_LIB}")
+
+# ---------------------------------------------------------------------------
+add_executable(live-caption-cli
+    src/main.cpp
+    src/transcript.cpp
+    src/qwen3asr.cpp
+    src/audio.cpp
+)
+
+target_include_directories(live-caption-cli PRIVATE src)
+
+target_link_libraries(live-caption-cli PRIVATE
+    Qt6::Core
+    Threads::Threads
+    PkgConfig::SAMPLERATE
+    PkgConfig::PULSE
+    ${LC_LLAMA_TARGET}
+    ${LC_MTMD_LIB}
+)
+
+if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
+    target_compile_options(live-caption-cli PRIVATE -Wall -Wextra -Wno-unused-parameter)
+endif()