- Add `AiSettingsCard` component and server actions for configuring an
OpenAI-compatible AI endpoint (e.g. OpenWebUI) from the admin panel
- Introduce `AiSettings` Prisma model with masked API key display and
connection testing UI
- Track `completedAt` on todos with a migration and backfill for existing
completed items
- Surface `createdAt`, `updatedAt`, and `completedAt` in the todo edit
dialog via a new `formatDateTime` utility
- Update `TodoDTO`, `getBoard`, `createTodo`, `toggleTodo`, and the board
context to carry and optimistically update timestamp fields
- Add `Select` UI component built on `@base-ui/react`