Add self-hosted kids calendar app

Express + SQLite (node:sqlite, no native build step) family calendar:
parent accounts with household invites, per-child calendars with
save/duplicate/print, a token-gated read-only kiosk view for tablets,
and polling to keep parent and kiosk views in sync. Defaults to port 3007.

Dockerfile

@@ -0,0 +1,16 @@
+FROM node:22-alpine
+
+WORKDIR /app
+
+COPY package.json ./
+RUN npm install --omit=dev
+
+COPY . .
+
+ENV PORT=3007
+ENV DATA_DIR=/app/data
+VOLUME ["/app/data"]
+
+EXPOSE 3007
+
+CMD ["node", "server.js"]