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。

src/core/transcript.cpp

@@ -0,0 +1,79 @@
+#include "transcript.h"
+
+#include <algorithm>
+#include <cctype>
+
+namespace lc {
+
+namespace {
+
+std::string trim(const std::string & s)
+{
+    const auto notSpace = [](unsigned char c) { return !std::isspace(c); };
+    auto begin = std::find_if(s.begin(), s.end(), notSpace);
+    auto end   = std::find_if(s.rbegin(), s.rend(), notSpace).base();
+    if (begin >= end) return {};
+    return std::string(begin, end);
+}
+
+} // namespace
+
+ParsedTranscript parseAsrOutput(const std::string & raw)
+{
+    ParsedTranscript out;
+
+    static const std::string kMarker = "<asr_text>";
+    const std::string trimmed = trim(raw);
+
+    const auto markerPos = trimmed.rfind(kMarker);
+    std::string head;
+    if (markerPos != std::string::npos) {
+        head       = trimmed.substr(0, markerPos);
+        out.text   = trimmed.substr(markerPos + kMarker.size());
+    } else {
+        head     = trimmed;
+        out.text = trimmed;
+    }
+
+    // 头部里找 "language <Name>"
+    // 允许前面有空白，语言名只取连续的字母
+    const std::string key = "language";
+    auto pos = head.find(key);
+    if (pos != std::string::npos) {
+        pos += key.size();
+        while (pos < head.size() && std::isspace(static_cast<unsigned char>(head[pos]))) ++pos;
+        size_t end = pos;
+        while (end < head.size() && std::isalpha(static_cast<unsigned char>(head[end]))) ++end;
+        out.language = head.substr(pos, end - pos);
+    }
+
+    out.text = trim(out.text);
+    return out;
+}
+
+std::string languageDisplayName(const std::string & lang)
+{
+    if (lang.empty()) return {};
+
+    static const struct { const char * key; const char * display; } kMap[] = {
+        { "English",    "英语" },
+        { "Chinese",    "中文" },
+        { "Japanese",   "日语" },
+        { "Korean",     "韩语" },
+        { "French",     "法语" },
+        { "German",     "德语" },
+        { "Spanish",    "西班牙语" },
+        { "Russian",    "俄语" },
+        { "Italian",    "意大利语" },
+        { "Portuguese", "葡萄牙语" },
+        { "Arabic",     "阿拉伯语" },
+        { "Cantonese",  "粤语" },
+    };
+
+    for (const auto & e : kMap) {
+        if (lang == e.key) return e.display;
+    }
+    return lang;
+}
+
+} // namespace lc