[dashboard] No way for consumer modules to contribute cards/widgets to the bundled dashboard #203

Summary

The bundled dashboard module renders a fixed set of cards (stats.py returns a hardcoded dict; module.py exposes only register_routes + register_menu_items). There's no registry or lifecycle hook for a consumer module to contribute a dashboard card/widget, so any app-specific dashboard content must be a separate page.

Environment

• Framework checkout: v0.0.17-5-g2b079c9; smpy / published simple_module_* / @simple-module-py/*: 0.0.17
• Python 3.12.3, uv 0.11.7, node v24.15.0, Linux (Ubuntu)

Found while building a real consumer app (Invoice Manager) on the framework.

Impact

For this Invoice Manager I had to build a separate per-currency dashboard inside the invoices module rather than contributing tiles to the bundled one. A register_dashboard_cards(registry) style hook (mirroring register_menu_items/register_permissions) would let modules add cards to the shared dashboard.

Suggestion

Add a dashboard card/widget contribution registry + lifecycle hook, or document that the bundled dashboard is intentionally non-extensible and consumers should build their own.