feat(app): Flatpak options and fixes with updater

[yofukashino]

Summary

• What changed:
  • Now reloads if web update instead of tellling user to download from app center
  • Added option to open app center if managed flatpak package
• Why it is correct:
  Because web updates requite only reload and almost all software centers which support flatpak also supports the appstream url
• Risk:
  Added new safe protocol appstream: which can used to software links but they are curated mostly so quite safe

Verification

• Tests run:
  pnpm test and all the files I edited passed
• Manual checks:
  openExternalUrl opens the software center atleast via console
• Screenshots or recordings:

Checklist

• I understand every change in this PR.
• I can explain what it does and why it is correct.
• I disclosed any LLM coding help below.

LLM Disclosure

None

[yofukashino]

uses appstream://app.fluxer.FluxerCanary but that is not a flatpak id on flathub as of now so if none of the repos have the app, it just opens the software center home page