move tx detail caching into sync engine, cache during history sync

- new sync-tx-details.ts: extracts tx+receipt caching from get-details.ts
- sync-tx-history: calls syncTxDetails per transfer hash during sync
- get-details: remove on-the-fly viem fetch + DB write (now handled
  by sync); returns null placeholder
- index: import syncTxDetails; simplify getTransactionDetails handler

apps/desktop/src/lib/electrobun.ts

@@ -236,7 +236,11 @@ type RPC = {
 				response: string[]
 			}
 			evmCreateWallet: {
-				params: { name: string; phrase: string; passwordHash?: string }
+				params: {
+					name: string
+					phrase: string
+					passwordHash?: string
+				}
 				response: { id: string; name: string; createdAt: string }
 			}
 			evmListWallets: {