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.

.env.example

@@ -0,0 +1,18 @@
+# Copy to .env and fill in before running with docker-compose,
+# or export these yourself before `node server.js`.
+
+# Required: a long random string used to sign session cookies.
+# Generate one with: node -e "console.log(require('node:crypto').randomBytes(32).toString('hex'))"
+SESSION_SECRET=
+
+# Set to true once this is served over HTTPS (e.g. behind a reverse proxy).
+# Leave false for plain-HTTP LAN use, otherwise cookies won't be sent.
+COOKIE_SECURE=false
+
+# Set to true after your household(s) are created to stop accepting new signups.
+DISABLE_PUBLIC_SIGNUP=false
+
+# Only needed outside Docker if you want the SQLite file somewhere specific.
+# DATA_DIR=./data
+
+# PORT=3007