chore: better update ux

[tatoalo]

Encountered some weird updating UX in ph-code:

• red X on open when the app's boot check was still in-flight (screenshot)
• "Check now" doing nothing when an update was already downloaded, clicking "Check now" would silently get stuck. Now shows "Update vX.Y.Z ready to install" with a green checkmark as expected
• no download feedback, UI showed "Checking for updates..." the whole time. Now transitions to "Downloading update..." (both in the settings panel and the toast) as soon as the download begins (may be slow depending on CDN and user network)