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。

tests/tst_livepipeline.cpp

@@ -0,0 +1,127 @@
+#include <QtTest>
+
+#include <algorithm>
+#include <cmath>
+#include <vector>
+
+#include "fakeasr.h"
+#include "livepipeline.h"
+
+namespace {
+
+constexpr double kPi = 3.14159265358979323846;
+
+std::vector<float> tone(size_t samples, float amplitude)
+{
+    std::vector<float> v(samples);
+    for (size_t i = 0; i < samples; ++i) {
+        v[i] = amplitude * (float) std::sin(2.0 * kPi * 440.0 * (double) i / 16000.0);
+    }
+    return v;
+}
+
+size_t totalSamples(const std::vector<size_t> & v)
+{
+    size_t n = 0;
+    for (size_t s : v) n += s;
+    return n;
+}
+
+lc::LivePipelineOptions options()
+{
+    lc::LivePipelineOptions o;
+    o.stream.chunkSec = 0.5;   // 0.5s 一块，测试里能快些触发
+    return o;
+}
+
+} // namespace
+
+// 实时管线的回归测试（用 FakeAsr + 直接喂音频，不碰 PulseAudio）。
+class TstLivePipeline : public QObject {
+    Q_OBJECT
+
+private slots:
+    // 静音不能送进模型。
+    // 曾经把采集到的静音也喂了进去，模型对静音产生幻觉（英文语音前冒出一个"嗯。"）。
+    void silenceIsNotForwarded()
+    {
+        FakeAsr fake;
+        lc::LivePipeline pipeline(fake, options());
+
+        const auto silence = tone(16000 * 3, 0.001f);   // 3s 背景噪声
+        pipeline.process(silence.data(), silence.size());
+
+        QCOMPARE(fake.samplesSeen.size(), size_t(0));
+    }
+
+    // 不丢样本。
+    // 曾经每次只处理 floor(可用/320) 帧并丢掉余数，每轮丢约 160 个样本，
+    // 造成假静音和句子被截断。
+    void noSamplesDroppedAcrossIrregularChunks()
+    {
+        FakeAsr fake;
+        lc::LivePipeline pipeline(fake, options());
+
+        const auto speech = tone(16000 * 10, 0.1f);   // 10s 语音
+        const size_t sizes[] = {1000, 7, 3333, 999, 12345, 1};
+
+        size_t off = 0;
+        int    i   = 0;
+        while (off < speech.size()) {
+            const size_t n = std::min(sizes[i++ % 6], speech.size() - off);
+            pipeline.process(speech.data() + off, n);
+            off += n;
+        }
+
+        const size_t forwarded = totalSamples(fake.samplesSeen);
+        // 允许剩下的不足一块留在引擎里（< 0.5s），其余都必须送到
+        QVERIFY2(forwarded >= 16000 * 9,
+                 qPrintable(QString("只送到了 %1 个样本（共 %2）")
+                                .arg(forwarded).arg(speech.size())));
+    }
+
+    // 静音够久要收束这一段（提交文本并重置上下文）
+    void silenceEndsSegment()
+    {
+        FakeAsr fake;
+        fake.scripted = {"a b c d e f"};
+
+        lc::LivePipeline pipeline(fake, options());
+        QString lastCommitted;
+        pipeline.setCaptionCallback(
+            [&lastCommitted](const std::string & committed, const std::string &,
+                             const std::string &) {
+                lastCommitted = QString::fromStdString(committed);
+            });
+
+        const auto speech = tone(16000 * 1, 0.1f);
+        pipeline.process(speech.data(), speech.size());
+        const int resetsAfterSpeech = fake.resets;
+
+        const auto silence = tone(16000 * 2, 0.001f);
+        pipeline.process(silence.data(), silence.size());
+
+        QVERIFY2(fake.resets > resetsAfterSpeech, "静音后没有收束这一段");
+        QVERIFY(!pipeline.inSegment());
+    }
+
+    // 语音之后继续有语音：不应该被切断成很多段
+    void continuousSpeechStaysInOneSegment()
+    {
+        FakeAsr fake;
+        lc::LivePipeline pipeline(fake, options());
+        const int resetsAfterConstruct = fake.resets;   // 构造 StreamingAsr 时会 reset 一次
+
+        const auto speech = tone(16000 * 4, 0.1f);
+        for (size_t off = 0; off < speech.size(); off += 4000) {
+            const size_t n = std::min(size_t(4000), speech.size() - off);
+            pipeline.process(speech.data() + off, n);
+        }
+
+        QVERIFY(pipeline.inSegment());
+        QCOMPARE(fake.resets, resetsAfterConstruct);
+    }
+};
+
+QTEST_MAIN(TstLivePipeline)
+#include "tst_livepipeline.moc"