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/platform/platform.go

@@ -0,0 +1,6 @@
+//go:build !windows
+
+package platform
+
+// EnableResizeBorder is a no-op on non-Windows platforms.
+func EnableResizeBorder() {}