refactor: split core/ui/apps targets and add unit tests

Move all business logic into liblivecaption_core (no Qt dependency) and
the widgets into liblivecaption_ui, leaving two executables: the caption
window and the CLI, which no longer links Qt Widgets. Abstract the ASR
backend behind IAsr so the streaming policy and the live pipeline can be
tested with a scripted fake backend instead of a real model.

把全部业务逻辑下沉到不依赖 Qt 的 liblivecaption_core，界面独立成
liblivecaption_ui，拆出悬浮窗与命令行两个可执行程序（CLI 不再链接 Qt
Widgets）；并用 IAsr 抽象推理后端，使流式策略与实时管线可脱离真模型
用假实现做单元测试。测试还抓到一个真 bug：段恰好结束在 chunk 边界时
只提交了稳定部分，最后几个词被丢掉，已修。

CMakeLists.txt

@@ -4,10 +4,13 @@ project(live-caption LANGUAGES CXX)
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+set(CMAKE_AUTOMOC ON)
 if(NOT CMAKE_BUILD_TYPE)
     set(CMAKE_BUILD_TYPE Release CACHE STRING "" FORCE)
 endif()
 
+option(LC_BUILD_TESTS "构建单元测试" ON)
+
 # ---------------------------------------------------------------------------
 # llama.cpp / libmtmd 的搜索路径
 #
@@ -29,8 +32,6 @@ find_package(Qt6 REQUIRED COMPONENTS Core Widgets)
 find_package(PkgConfig REQUIRED)
 find_package(Threads REQUIRED)
 
-set(CMAKE_AUTOMOC ON)
-
 pkg_check_modules(SAMPLERATE REQUIRED IMPORTED_TARGET samplerate)
 pkg_check_modules(PULSE      REQUIRED IMPORTED_TARGET libpulse)
 
@@ -47,37 +48,32 @@ else()
         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_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)
+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/streamingasr.cpp
-    src/audio.cpp
-    src/livetranscriber.cpp
-    src/captionwindow.cpp
+# core：全部业务逻辑，刻意不依赖 Qt（方便测试与复用）
+# ---------------------------------------------------------------------------
+add_library(livecaption_core STATIC
+    src/core/transcript.cpp
+    src/core/audio.cpp
+    src/core/qwen3asr.cpp
+    src/core/streamingasr.cpp
+    src/core/livepipeline.cpp
 )
-
-target_include_directories(live-caption-cli PRIVATE src)
-
-target_link_libraries(live-caption-cli PRIVATE
-    Qt6::Core
-    Qt6::Widgets
+target_include_directories(livecaption_core PUBLIC src/core)
+target_link_libraries(livecaption_core PUBLIC
     Threads::Threads
     PkgConfig::SAMPLERATE
     PkgConfig::PULSE
@@ -85,6 +81,37 @@ target_link_libraries(live-caption-cli PRIVATE
     ${LC_MTMD_LIB}
 )
 
+# ---------------------------------------------------------------------------
+# ui：悬浮窗与 Qt 适配层
+# ---------------------------------------------------------------------------
+add_library(livecaption_ui STATIC
+    src/ui/captionwindow.cpp
+    src/ui/livetranscriber.cpp
+)
+target_include_directories(livecaption_ui PUBLIC src/ui)
+target_link_libraries(livecaption_ui PUBLIC livecaption_core Qt6::Widgets)
+
+# ---------------------------------------------------------------------------
+# 可执行程序
+# ---------------------------------------------------------------------------
+# GUI：悬浮字幕窗
+add_executable(live-caption apps/gui/main.cpp)
+target_include_directories(live-caption PRIVATE apps/common)
+target_link_libraries(live-caption PRIVATE livecaption_ui)
+
+# CLI：文件 / 流式文件 / 命令行实时；不链接 Qt Widgets
+add_executable(live-caption-cli apps/cli/main.cpp)
+target_include_directories(live-caption-cli PRIVATE apps/common)
+target_link_libraries(live-caption-cli PRIVATE livecaption_core Qt6::Core)
+
 if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
-    target_compile_options(live-caption-cli PRIVATE -Wall -Wextra -Wno-unused-parameter)
+    foreach(_t livecaption_core livecaption_ui live-caption live-caption-cli)
+        target_compile_options(${_t} PRIVATE -Wall -Wextra -Wno-unused-parameter)
+    endforeach()
+endif()
+
+# ---------------------------------------------------------------------------
+if(LC_BUILD_TESTS)
+    enable_testing()
+    add_subdirectory(tests)
 endif()