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/db.rs

@@ -10,7 +10,7 @@ const MAX_BACKUPS: usize = 10;
 const BACKUP_PREFIX: &str = "voiced-pre-v";
 
 /// Highest schema version, i.e. the number of entries in `migrations()`.
-const LATEST_VERSION: i64 = 7;
+const LATEST_VERSION: i64 = 8;
 
 #[derive(Debug, thiserror::Error)]
 pub enum DbError {
@@ -245,8 +245,36 @@ CREATE TABLE item_presets (
 );
 "#;
 
+/// Version 8: payments received against issued invoices. Amounts are integer paise. `amount_paise` is the cash
+/// received and `tds_paise` the tax the client deducted at source; both count towards settling the invoice.
+/// Payment status is derived from these rows and the due date, never stored, and the issued invoice row is untouched.
+const M8: &str = r#"
+CREATE TABLE payments (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    invoice_id   INTEGER NOT NULL REFERENCES invoices(id),
+    paid_on      TEXT NOT NULL,
+    amount_paise INTEGER NOT NULL DEFAULT 0 CHECK (amount_paise >= 0),
+    tds_paise    INTEGER NOT NULL DEFAULT 0 CHECK (tds_paise >= 0),
+    mode         TEXT NOT NULL CHECK (mode IN ('bank_transfer', 'upi', 'cash', 'cheque', 'other')),
+    reference    TEXT NOT NULL DEFAULT '',
+    notes        TEXT NOT NULL DEFAULT '',
+    created_at   TEXT NOT NULL,
+    CHECK (amount_paise + tds_paise > 0)
+);
+CREATE INDEX idx_payments_invoice ON payments(invoice_id);
+"#;
+
 fn migrations() -> Migrations<'static> {
-    Migrations::new(vec![M::up(SCHEMA), M::up(M2), M::up(M3), M::up(M4), M::up(M5), M::up(M6), M::up(M7)])
+    Migrations::new(vec![
+        M::up(SCHEMA),
+        M::up(M2),
+        M::up(M3),
+        M::up(M4),
+        M::up(M5),
+        M::up(M6),
+        M::up(M7),
+        M::up(M8),
+    ])
 }
 
 /// Open (creating if needed) the database at `path` and bring it to the latest schema.
@@ -725,7 +753,7 @@ CREATE INDEX IF NOT EXISTS idx_invoices_created ON invoices(created_at DESC);
         .unwrap();
 
         migrations().to_latest(&mut conn).unwrap();
-        assert_eq!(user_version(&conn), 7);
+        assert_eq!(user_version(&conn), LATEST_VERSION);
 
         type Row = (String, String, String, String, String, String, String);
         let rows: Vec<Row> = conn