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.

.gitignore

@@ -0,0 +1,4 @@
+node_modules/
+data/
+.env
+*.log