v0.1.0

feat(gui): add step-based guidance and smarter track chooser

Guide first-time users through a numbered flow (drop files, pick
reference track, align). Hide the embedded-track dropdown until files
are added, show only a note when a video has a single track, and
highlight the chooser with a clear prompt when multiple tracks exist.
Add a one-line tagline, make the Align button prominent, and keep all
new labels bilingual with runtime language switching.