chore: point homepage metadata at proton-drive.narl.io

The About dialog's website link, the README, and the package metadata
(Cargo, PKGBUILDs, AUR .SRCINFO, .deb, .rpm) now use the project
homepage. Source code, issue, and release links stay on GitHub.

README.md

@@ -8,6 +8,8 @@
 local folders, Photos, sharing, and a native GTK4 app with tray and search launcher, plus a
 scriptable CLI.
 
+**[proton-drive.narl.io](https://proton-drive.narl.io)**
+
 [![CI](https://github.com/narrrl/proton-drive-linux/actions/workflows/ci.yml/badge.svg)](https://github.com/narrrl/proton-drive-linux/actions/workflows/ci.yml)
 [![Release](https://img.shields.io/github/v/release/narrrl/proton-drive-linux?sort=semver)](https://github.com/narrrl/proton-drive-linux/releases/latest)
 [![AUR](https://img.shields.io/aur/version/proton-drive-for-linux)](https://aur.archlinux.org/packages/proton-drive-for-linux)