docs(cli): show option default values in --help

Qt does not print default values in --help output; the default passed to
the option constructor is only a fallback for value(). Append them to
the descriptions instead, via one shared helper used by both programs.

Qt 不会把默认值印进 --help（构造参数里的默认值只作为 value() 的兜底），
改为在说明后拼上「（默认 X）」；两个程序共用同一处定义，并统一了措辞。

apps/common/appcli.h

@@ -12,24 +12,39 @@
 // 两个可执行程序（GUI / CLI）共用的命令行选项定义与解析。
 namespace lc::app {
 
+// 构造命令行选项。
+//
+// Qt 自己不会把默认值印进 --help（构造函数里传的默认值只作为 value() 的兜底），
+// 所以这里在给了默认值时把「（默认 X）」拼到说明后面。
+inline QCommandLineOption makeOption(const QString & name, const QString & description,
+                                     const QString & valueName = QString(),
+                                     const QString & defaultValue = QString())
+{
+    QString desc = description;
+    if (!defaultValue.isEmpty()) {
+        desc += QStringLiteral("（默认 %1）").arg(defaultValue);
+    }
+    if (valueName.isEmpty()) return QCommandLineOption(name, desc);
+    return QCommandLineOption(name, desc, valueName, defaultValue);
+}
+
 inline void addModelOptions(QCommandLineParser & p)
 {
-    p.addOption(QCommandLineOption("model", "主模型 GGUF 路径（架构须为 qwen3vl）", "path"));
+    p.addOption(makeOption("model", "主模型 GGUF 路径（架构须为 qwen3vl）", "path"));
-    p.addOption(QCommandLineOption("mmproj", "mmproj GGUF 路径（clip + qwen3a）", "path"));
+    p.addOption(makeOption("mmproj", "mmproj GGUF 路径（clip + qwen3a）", "path"));
-    p.addOption(QCommandLineOption("threads", "推理线程数", "n", "8"));
+    p.addOption(makeOption("threads", "推理线程数", "n", "8"));
-    p.addOption(QCommandLineOption("max-tokens", "单段最多生成 token 数", "n", "256"));
+    p.addOption(makeOption("max-tokens", "单段最多生成 token 数", "n", "256"));
-    p.addOption(QCommandLineOption("verbose", "输出 llama.cpp/mtmd 的详细日志"));
+    p.addOption(makeOption("verbose", "输出 llama.cpp/mtmd 的详细日志"));
 }
 
 inline void addStreamOptions(QCommandLineParser & p)
 {
-    p.addOption(QCommandLineOption("stream-chunk", "流式 chunk 秒数", "sec", "2.0"));
+    p.addOption(makeOption("stream-chunk", "流式 chunk / 提交粒度，单位秒", "sec", "2.0"));
-    p.addOption(QCommandLineOption("stream-window", "滑窗上限秒数（仅 window 模式）", "sec", "16"));
+    p.addOption(makeOption("stream-window", "滑窗上限，单位秒；仅 window 模式，0=不滑窗", "sec", "16"));
-    p.addOption(QCommandLineOption("stream-segment", "单段最长秒数（0=不限）", "sec", "30"));
+    p.addOption(makeOption("stream-segment", "单段最长时长，单位秒；0=不限", "sec", "30"));
-    p.addOption(QCommandLineOption("unfixed-tokens", "前缀回滚丢弃的 token 数", "n", "5"));
+    p.addOption(makeOption("unfixed-tokens", "前缀回滚丢弃的 token 数", "n", "5"));
-    p.addOption(QCommandLineOption("unfixed-chunks", "冷启动不带前缀的 chunk 数", "n", "2"));
+    p.addOption(makeOption("unfixed-chunks", "冷启动不带前缀的 chunk 数", "n", "2"));
-    p.addOption(QCommandLineOption("stream-mode", "流式后端: incremental 或 window", "mode",
+    p.addOption(makeOption("stream-mode", "流式后端: incremental 或 window", "mode", "incremental"));
-                                   "incremental"));
 }
 
 inline AsrOptions asrOptions(const QCommandLineParser & p)

apps/gui/main.cpp

@@ -84,9 +84,9 @@ int main(int argc, char ** argv)
     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(lc::app::makeOption("opacity", "字幕背景不透明度，取值 20-100", "n", "84"));
-    parser.addOption(QCommandLineOption("screenshot", "启动后自动截图并退出（验证渲染用）", "path"));
+    parser.addOption(lc::app::makeOption("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.addOption(lc::app::makeOption("screenshot-delay", "截图前等待秒数", "sec", "6"));
     parser.process(app);
 
     const lc::AsrOptions asrOpt = lc::app::asrOptions(parser);