feat(launcher): add --version / -v flag to print app version

- Exits early with `SubMiner <version>` output, no app binary required
- Maps `-v` at root level without conflicting with `stats cleanup -v`
- Adds `version: boolean` to `Args` type and default args
- Documents flag in docs-site and adds changelog fragment

docs-site/usage.md

@@ -78,6 +78,8 @@ subminer -S video.mkv             # Same as above via --start-overlay
 subminer https://youtu.be/...     # Play a YouTube URL
 subminer ytsearch:"jp news"       # Play first YouTube search result
 subminer --setup                  # Open first-run setup popup
+subminer --version                # Print installed SubMiner version
+subminer -v                       # Same as above
 subminer --log-level debug video.mkv # Enable verbose logs for launch/debugging
 subminer --log-level warn video.mkv  # Set logging level explicitly
 subminer --args '--fs=opengl-hq --ytdl-format=bestvideo*+bestaudio/best' video.mkv  # Pass extra mpv args