[DRAFT] feat: add ShoppingList stacklet (Koffan) for shared family grocery lists

[yarmand]

summary

• Add the koffan stacklet running Koffan, a lightweight shared shopping-list web app, surfaced in famstack as "ShoppingList" on port 42090 with real-time sync and a PWA install.
• Auth uses a single family-shared password auto-generated into secrets.toml and shown via post-up hints; APP_ENV=development keeps login cookies working in port mode, and language/timezone are inherited from stack.toml.
• Pure declaration (manifest, single-service compose, caddy route) with SQLite on a bind mount; no hooks, CLI plugins, or bots.

missing

link to the AI piece of famstack.