[Projects]: Redirect to the invoice edit page after billing project tasks

[nielsdrost7]

ProjectBillingService::billTasks() (Modules/Projects/Services/ProjectBillingService.php) creates or appends to a draft invoice when tasks are billed via the bill_tasks row action on the projects list (Modules/Projects/Filament/Company/Resources/Projects/Tables/ProjectsTable.php). On success, the action only shows a "tasks billed to draft invoice" notification — it does not redirect the user to the resulting invoice.

This was a deliberate deviation in PR #578 because the invoice EditRecord page did not exist on develop yet at the time. The EditInvoice page now exists on develop (and is further extended by PR #575 / issue #542), so this follow-up is unblocked.

Acceptance criteria

• After a successful bill_tasks action, redirect the user to InvoiceResource::getUrl('edit', ['record' => $invoice]) (mirroring the pattern already used by EditInvoice's copy_invoice and create_credit_note actions).
• Notification still confirms the billing action before/at redirect.