feat: FFmpeg GUI desktop application

Wails v2 + Vue3 + Go project with:
- Encode/Remux/Subtitle burn with hardware acceleration
- Real-time progress with ffmpeg stderr parsing (\r delimiter handling)
- Task queue with cancel support
- Per-task log viewer with color-coded output
- Custom frameless window with resize support
- Dark/light theme toggle
- Hardware encoder detection (NVENC/QSV/AMF)

internal/ffmpeg/detector.go

@@ -0,0 +1,63 @@
+package ffmpeg
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+)
+
+// BinPaths holds paths to ffmpeg and ffprobe binaries.
+type BinPaths struct {
+	FFmpeg  string
+	FFprobe string
+}
+
+// Detect finds ffmpeg and ffprobe binaries.
+// Priority: 1. build/bin/ (bundled)  2. PATH
+func Detect() (BinPaths, error) {
+	exeDir, err := os.Executable()
+	if err != nil {
+		exeDir = "."
+	} else {
+		exeDir = filepath.Dir(exeDir)
+	}
+
+	bundled := BinPaths{
+		FFmpeg:  binPath(exeDir, "ffmpeg"),
+		FFprobe: binPath(exeDir, "ffprobe"),
+	}
+
+	// Check bundled first
+	if fileExists(bundled.FFmpeg) && fileExists(bundled.FFprobe) {
+		return bundled, nil
+	}
+
+	// Fall back to PATH
+	return findOnPath()
+}
+
+func binPath(baseDir, name string) string {
+	ext := ""
+	if runtime.GOOS == "windows" {
+		ext = ".exe"
+	}
+	return filepath.Join(baseDir, "build", "bin", name+ext)
+}
+
+func fileExists(path string) bool {
+	_, err := os.Stat(path)
+	return err == nil
+}
+
+func findOnPath() (BinPaths, error) {
+	ffmpeg, err := exec.LookPath("ffmpeg")
+	if err != nil {
+		return BinPaths{}, err
+	}
+	ffprobe, err := exec.LookPath("ffprobe")
+	if err != nil {
+		return BinPaths{}, err
+	}
+	return BinPaths{FFmpeg: ffmpeg, FFprobe: ffprobe}, nil
+}