Add README, plugin citations, and multi-platform release CI.

Ship screenshots and third-party notices for the desktop shell, and
package Windows, macOS, deb, rpm, and Flatpak from GitHub Releases.

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/capture-screenshots.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+OUT="$ROOT/docs/screenshots"
+SRC="$OUT/src"
+CHROME="${CHROME:-google-chrome}"
+
+capture() {
+  local name="$1"
+  local html="$2"
+  "$CHROME" \
+    --headless=new \
+    --disable-gpu \
+    --no-sandbox \
+    --hide-scrollbars \
+    --force-device-scale-factor=2 \
+    --window-size=1280,800 \
+    --default-background-color=00000000 \
+    --screenshot="$OUT/$name.png" \
+    "file://$html"
+  echo "wrote $OUT/$name.png"
+}
+
+mkdir -p "$OUT"
+capture splash "$SRC/splash.html"
+capture session "$SRC/session.html"
+capture vision "$SRC/vision.html"
+capture menu "$SRC/menu.html"
+cp -f "$ROOT/ui/icon.png" "$OUT/icon.png"