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。

apps/gui/main.cpp

@@ -0,0 +1,102 @@
+// 图形界面版：悬浮字幕窗。
+#include <cstdio>
+
+#include <QApplication>
+#include <QCommandLineOption>
+#include <QCommandLineParser>
+#include <QGuiApplication>
+#include <QTimer>
+
+#include "appcli.h"
+#include "captionwindow.h"
+#include "livetranscriber.h"
+#include "qwen3asr.h"
+#include "streamingasr.h"
+#include "transcript.h"
+
+namespace {
+
+int runGui(lc::Qwen3Asr & asr, const lc::StreamOptions & sop,
+           const QString & screenshotPath, int screenshotDelaySec, int opacityPercent)
+{
+    lc::CaptionWindow window;
+    window.setPanelOpacity(opacityPercent);
+    lc::LiveTranscriber live(asr);
+
+    QObject::connect(&live, &lc::LiveTranscriber::caption, &window,
+                     [&window](const QString & committed, const QString & tail,
+                               const QString & lang) {
+                         window.setLanguage(
+                             QString::fromStdString(lc::languageDisplayName(lang.toStdString())));
+                         window.setCaption(committed, tail);
+                     });
+    QObject::connect(&live, &lc::LiveTranscriber::failed, &window, [](const QString & m) {
+        qWarning("采集失败: %s", qUtf8Printable(m));
+    });
+    QObject::connect(&window, &lc::CaptionWindow::closed, qApp, &QCoreApplication::quit);
+    QObject::connect(&window, &lc::CaptionWindow::languageClicked, &window, [] {
+        qInfo() << "语言标签被点击（设置界面将在 Phase 4 接入）";
+    });
+
+    QString err;
+    if (!live.start(sop, &err)) {
+        qCritical("启动采集失败: %s", qUtf8Printable(err));
+        return 1;
+    }
+    qInfo("正在采集: %s", qUtf8Printable(live.deviceName()));
+
+    window.show();
+
+    if (!screenshotPath.isEmpty()) {
+        // 自截图：用于验证渲染（不依赖外部截图工具）
+        QTimer::singleShot(screenshotDelaySec * 1000, &window, [&window, screenshotPath] {
+            const bool ok1 = window.grab().save(screenshotPath);
+
+            window.setCollapsed(false);
+            QString expandedPath = screenshotPath;
+            expandedPath.replace(QStringLiteral(".png"), QStringLiteral("-expanded.png"));
+            const bool ok2 = window.grab().save(expandedPath);
+
+            std::fprintf(stderr, "截图: 折叠态 %s / 展开态 %s\n",
+                         ok1 ? "成功" : "失败", ok2 ? "成功" : "失败");
+            QCoreApplication::quit();
+        });
+    }
+
+    return QCoreApplication::exec();
+}
+
+} // namespace
+
+int main(int argc, char ** argv)
+{
+    // 说明意图：DPI 取整策略必须在 QGuiApplication 之前定。
+    // （Deepin 的会话环境已经设了 QT_SCALE_FACTOR_ROUNDING_POLICY，
+    //   所以本机仍会看到 Qt 的那条提醒，那不是本程序的问题。）
+    QGuiApplication::setHighDpiScaleFactorRoundingPolicy(
+        Qt::HighDpiScaleFactorRoundingPolicy::PassThrough);
+
+    QApplication app(argc, argv);
+    QCoreApplication::setApplicationName(QStringLiteral("live-caption"));
+
+    QCommandLineParser parser;
+    parser.setApplicationDescription(QStringLiteral("实时字幕（悬浮窗）"));
+    parser.addHelpOption();
+    lc::app::addModelOptions(parser);
+    lc::app::addStreamOptions(parser);
+    parser.addOption(QCommandLineOption("opacity", "字幕背景不透明度（20-100，百分比）", "n", "84"));
+    parser.addOption(QCommandLineOption("screenshot", "启动后自动截图并退出（验证渲染用）", "path"));
+    parser.addOption(QCommandLineOption("screenshot-delay", "截图前等待秒数", "sec", "6"));
+    parser.process(app);
+
+    const lc::AsrOptions asrOpt = lc::app::asrOptions(parser);
+    const lc::StreamOptions sop = lc::app::streamOptions(parser);
+
+    lc::Qwen3Asr asr;
+    if (!lc::app::loadModel(asr, asrOpt)) return 1;
+
+    return runGui(asr, sop,
+                  parser.value("screenshot"),
+                  parser.value("screenshot-delay").toInt(),
+                  parser.value("opacity").toInt());
+}