Add payments with TDS, invoice detail view and filterable History (Phase E2)

- Migration M8 adds payments (cash, TDS, mode, reference). Payment status is derived, never stored: unpaid, partially paid, paid, or overdue. Overpayment is rejected, TDS counts toward settling, and only issued invoices accept payments. list_invoices and get_invoice carry the paid, TDS and balance summary.
- New invoice detail view: archived-PDF preview, payments list, Record payment modal, Export, Duplicate (as a draft), Re-render and Cancel. An invoice with payments cannot be cancelled until they are deleted.
- History gets search, status, financial-year, month and client filters, sortable columns, pagination, footer totals and an FY summary. Cancelled invoices are excluded from totals. The per-row archive-status calls are gone; archiving is on the detail page.
- Rust tests for payments and the list summary; vitest for fiscal-year, money, filter and duplicate helpers.

PDF output and fingerprint goldens are unchanged. The new UI has not been run in a webview yet.

src-tauri/src/lib.rs

@@ -133,6 +133,9 @@ pub fn run() {
             commands::invoice::list_drafts,
             commands::invoice::get_draft,
             commands::invoice::delete_draft,
+            commands::payments::record_payment,
+            commands::payments::list_payments,
+            commands::payments::delete_payment,
             commands::assets::import_asset,
             commands::assets::save_asset_bytes,
             commands::assets::read_asset_data_uri,