feat: click a coin row to view its trade history; edit transactions

Matches CoinMarketCap's flow: clicking anywhere on a coin's row in the
holdings table opens its transaction history (previously only a dedicated
icon button did). The table's own History icon is gone since the row now
does that job; the remaining "+"/delete icons get stopPropagation so they
don't also trigger the row click.

Adds the missing piece: transactions could be viewed and deleted but not
edited. New PATCH /crypto/transactions/{id} (partial update, never calls
CoinGecko, same oversell guard as creating a sell) backs a pencil button on
each history row that opens CryptoTransactionModal pre-filled — the same
dialog used for "+", now doing double duty as create/edit.

86/86 backend tests passing (4 new). Verified live against the real API:
create, edit quantity/note, 404 on unknown id, cleanup — real user data
untouched throughout.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01855PiW5Wd8n4aRW4n9kByY

frontend/src/api/crypto.ts

@@ -33,6 +33,10 @@ export function fetchCryptoTransactions(assetId: number) {
   return api.get<CryptoTransaction[]>(`/crypto/holdings/${assetId}/transactions`);
 }
 
+export function updateCryptoTransaction(transactionId: number, input: CryptoTransactionInput) {
+  return api.patch<CryptoHolding>(`/crypto/transactions/${transactionId}`, input);
+}
+
 export function deleteCryptoTransaction(transactionId: number) {
   return api.delete<void>(`/crypto/transactions/${transactionId}`);
 }