feat(cash): mark how a transaction was paid, exclude cash from reconciliation

getPendingReconciliations treated every unreconciled manual transaction as
awaiting a matching statement row. Cash never appears on a statement, so a cash
entry sat in the queue indefinitely being offered matches within 3 days and 1%
on amount - and accepting one is silently destructive: reconciled manual rows
are filtered out of every query, so the cash spend disappears while the card
transaction it matched claims to be that same spend.

Migration 0016 adds transactions.payment_method (card | cash | bank_transfer |
other, NULL = unknown) with a CHECK constraint and a partial index. The notCash()
fragment excludes cash from both halves of the reconciliation query - the pending
list and the candidate match subquery, which aliases the manual row as m.

Only cash is excluded. Bank transfers do appear on a statement now that
transaction accounts are imported, and NULL means unknown, so both stay
candidates and every pre-existing row behaves exactly as before.

ATM withdrawals deliberately stay categorised as spend rather than transfers.
Treating them as transfers is only correct if every cash purchase is logged;
with partial logging it silently deletes the unlogged remainder from spend.

src/components/add-transaction-modal.tsx

@@ -35,6 +35,8 @@ export function AddTransactionModal({
   const [type, setType] = useState(prefill?.transaction_type ?? "debit");
   const [merchant, setMerchant] = useState(prefill?.merchant_normalized ?? "");
   const [category, setCategory] = useState(prefill?.category ?? "");
+  // Cash is excluded from reconciliation — it will never appear on a statement.
+  const [paymentMethod, setPaymentMethod] = useState("");
   const [selectedTagIds, setSelectedTagIds] = useState<number[]>([]);
   const [splits, setSplits] = useState<{ participant_id: number; share_percent: number }[]>(
     prefill?.splits ?? []
@@ -68,6 +70,7 @@ export function AddTransactionModal({
       transaction_type: type,
       merchant_normalized: merchant || undefined,
       category: category || undefined,
+      payment_method: paymentMethod || undefined,
       splits: splits.length ? splits : undefined,
     });
     if (selectedTagIds.length && result?.id) {
@@ -159,6 +162,26 @@ export function AddTransactionModal({
             </div>
           </div>
 
+          <div>
+            <label className="block text-xs text-zinc-500 mb-1">Paid by</label>
+            <select
+              value={paymentMethod}
+              onChange={(e) => setPaymentMethod(e.target.value)}
+              className="w-full bg-zinc-800 border border-zinc-700 rounded px-2 py-1.5 text-sm"
+            >
+              <option value="">— unknown —</option>
+              <option value="card">Card</option>
+              <option value="cash">Cash</option>
+              <option value="bank_transfer">Bank transfer</option>
+              <option value="other">Other</option>
+            </select>
+            {paymentMethod === "cash" && (
+              <p className="text-[11px] text-zinc-500 mt-1">
+                Cash won&apos;t be offered for reconciliation — it never appears on a statement.
+              </p>
+            )}
+          </div>
+
           <div>
             <label className="block text-xs text-zinc-500 mb-1">Merchant (optional)</label>
             <input