fix: change badge count type from usize to i64 in update_taskbar_badg…

…e function

feat: update version to 0.2.16 across all relevant files

chore: update version to 0.2.15 and enhance changelog with new features

feat: add Flatpak preflight validation script for build checks

feat: update version to 0.2.13 in package.json and package-lock.json

feat: update app version to 0.2.12 in +page.svelte

fix: update Flatpak image and runtime version to gnome-48

fix: update version to 0.2.10 in various project files

feat: add flatpak-cargo-generator script for managing Flatpak depende…

…ncies

fix: update version to 0.2.8 in package.json