[Invoices]: Invoice edit/detail page (EditRecord)

[nielsdrost7]

Context

InvoiceResource currently only has ListInvoices and CreateInvoice pages. There is no way to open a specific invoice for editing. A dedicated EditRecord page is required to house the invoice form and the status-dependent action bar described in #223 (draft) and #224 (paid).

Invoices are too complex for a slide-over (line items, tax calculation, totals, credit notes) — a full page is the right pattern here, matching InvoicePlane v1 behaviour.

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User story

As a user, I want to open a specific invoice in a full edit page so I can modify line items, adjust dates, view calculated totals, and trigger invoice actions (download, send, copy, credit note) from the top-right header bar.

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Acceptance criteria

• Modules/Invoices/Filament/Company/Resources/Invoices/Pages/EditInvoice.php extends EditRecord
• Registered in InvoiceResource::getPages() as 'edit' => EditInvoice::route('/{record}/edit')
• Invoice list row action "Edit" navigates to this page
• The full invoice form is rendered on the page (same schema as CreateInvoice)
• getHeaderActions() skeleton exists and is ready for [Invoices]: Action dropdown on draft invoice edit screen #223 and [Invoices]: Action dropdown on paid invoice edit screen #224 to populate
• After save, user stays on the edit page (standard Filament EditRecord behaviour)

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Parent of #223 (draft invoice actions) and #224 (paid invoice actions).
Child of the Invoices Epic #15.