Add billedToTenant property to Bill interface with UI support

Added new boolean property to track whether a bill should be paid by the tenant.

Changes:
- Added billedToTenant property to Bill interface in db-types.ts
- Added checkbox UI control in BillEditForm for billedToTenant
- Added state management and change handler for the checkbox
- Added i18n translations (EN: "Billed to tenant", HR: "Plaća podstanar")
- Set default value to true for new bills

Note: Server action implementation pending - property not yet persisted to database.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/lib/db-types.ts

@@ -38,6 +38,8 @@ export interface Bill {
     name: string;
     /** is the bill paid */
     paid: boolean;
+    /** true if tenant to cover the bill */
+    billedToTenant: boolean;
     /** payed amount amount in cents */
     payedAmount?: number | null;
     /** attached document (optional) */