add automated screenshots, fastlane metadata, and appstream metainfo

Fixes #174, fixes #173, fixes #172

linux/nix/screenshots.sh

@@ -0,0 +1,30 @@
+# shellcheck shell=bash
+
+# Regenerates the README, AppStream and Fastlane screenshots, from
+# integration_test/screenshots. Run it from the repo root.
+
+work="$(mktemp -d)"
+# shellcheck disable=SC2329 # Run by the trap
+cleanup() { rm -rf "$work"; }
+trap cleanup EXIT
+
+GOCACHE="$(go env GOCACHE)"
+export GOCACHE
+
+XDG_DATA_HOME="$work/data" XDG_CACHE_HOME="$work/cache" \
+    dbus-run-session -- \
+    flutter test integration_test/screenshots/screenshots_test.dart -d linux \
+    --dart-define="SCREENSHOTS_DIR=$work/out" "$@"
+
+for shot in "$work"/out/*.png; do
+    pngquant --quality 65-95 --speed 1 --strip --force --ext .png "$shot"
+    oxipng --quiet --opt 4 --strip safe "$shot"
+done
+
+install -Dm644 "$work"/out/desktop-*.png -t assets/screenshots
+
+phone=fastlane/metadata/android/en-US/images/phoneScreenshots
+install -Dm644 "$work/out/phone-chat-light.png" "$phone/1.png"
+install -Dm644 "$work/out/phone-chat-dark.png" "$phone/2.png"
+install -Dm644 "$work/out/phone-rooms-light.png" "$phone/3.png"
+install -Dm644 "$work/out/phone-rooms-dark.png" "$phone/4.png"