Add streaming progress support to Deno upgrades and hook it into the GUI. upgrade_deno() now accepts an optional progress_callback and uses subprocess.Popen to read stdout line-by-line (line-buffered, utf-8, errors replaced), collecting output and invoking the callback as lines arrive. Added DenoUpdateThread (QThread) with finished/progress/error signals and replaced the previous background thread usage in the updater UI with this QThread. GUI slots strip ANSI escapes, truncate long messages, and update status text; buttons are re-enabled on finish/error. Improved logging and error handling for upgrade failures.
Initialize an error buffer and collect yt-dlp "ERROR:" output lines during direct command runs. When the process exits non‑zero, emit a more informative error using the last two captured error lines (falling back to the generic return-code message if none were captured). Also ensure the buffer is present before appending and keep the existing delay/cleanup flow.
Renamed 'src/core' to 'ytsage/core' and updated all internal imports to use relative paths. This improves package structure and ensures correct module resolution after the directory move.