Auto-resolve FX rate on account creation (base=1, else fetch from API)

Account creation no longer requires the user to enter an FX rate.
On create:
  - If account currency == company base → fxRateToBase = 1
  - Otherwise → fetchRate(accountCurrency, baseCurrency) from the
    fawazahmed0 FX API (same helper the daily scheduler uses)
  - Fallback to 1 if API call fails
The manual override field is still shown on the edit form for admin
corrections, and the daily scheduler keeps it fresh.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/routes/(app)/companies/[companyId]/accounts/+page.server.ts

@@ -2,6 +2,7 @@ import { error, fail } from '@sveltejs/kit';
 import type { Actions, PageServerLoad } from './$types';
 import { db } from '$lib/server/db/index.js';
 import {
+	companies,
 	companyAccounts,
 	companyAccountTransactions,
 	externalAccounts
@@ -13,8 +14,26 @@ import {
 	postTransfer,
 	type CompanyAccountTxnType
 } from '$lib/server/accounts/ledger.js';
+import { fetchRate } from '$lib/server/fx/index.js';
 import { and, asc, eq, isNull, sql } from 'drizzle-orm';
 
+async function resolveFxRate(companyId: string, accountCurrency: string): Promise<string> {
+	const [company] = await db
+		.select({ currency: companies.currency })
+		.from(companies)
+		.where(eq(companies.id, companyId))
+		.limit(1);
+	const base = company?.currency ?? 'THB';
+	if (accountCurrency.toUpperCase() === base.toUpperCase()) return '1';
+	try {
+		const rate = await fetchRate(accountCurrency, base);
+		if (rate !== null && rate > 0) return rate.toFixed(8);
+	} catch {
+		// fall through
+	}
+	return '1';
+}
+
 const MANUAL_TXN_TYPES = ['deposit', 'adjustment'] as const;
 type ManualTxnType = (typeof MANUAL_TXN_TYPES)[number];
 
@@ -281,6 +300,9 @@ export const actions: Actions = {
 		const openingBalanceDate =
 			parseDate(fd.get('openingBalanceDate')) ?? new Date();
 
+		// Auto-determine FX rate: 1 for base currency, API rate otherwise
+		const fxRateToBase = await resolveFxRate(params.companyId, f.currency);
+
 		const inserted = await db.transaction(async (tx) => {
 			const [row] = await tx
 				.insert(companyAccounts)
@@ -306,7 +328,7 @@ export const actions: Actions = {
 					creditLimit: f.creditLimit,
 					statementCloseDay: f.statementCloseDay,
 					paymentDueDay: f.paymentDueDay,
-					fxRateToBase: f.fxRateToBase,
+					fxRateToBase,
 					externalAccountId: f.externalAccountId
 				})
 				.returning({ id: companyAccounts.id });

src/routes/(app)/companies/[companyId]/accounts/+page.svelte

@@ -177,6 +177,7 @@
 				class={inputCls}
 			/>
 		</div>
+		{#if prefix.startsWith('edit-')}
 			<div>
 				<label for="{prefix}-fxRate" class={labelCls}>FX Rate to Base</label>
 				<input
@@ -189,8 +190,13 @@
 					placeholder="1.0 for THB, 34.5 for USD→THB"
 					class={inputCls}
 				/>
-			<p class="mt-0.5 text-xs text-gray-400 dark:text-gray-500">1.0 if same as company currency</p>
+				<p class="mt-0.5 text-xs text-gray-400 dark:text-gray-500">Auto-refreshed daily from FX API. Override here to override.</p>
 			</div>
+		{:else}
+			<div class="text-xs text-gray-500 dark:text-gray-400 self-end pb-2">
+				FX rate: auto-set on create (1 if base currency, else fetched from FX API)
+			</div>
+		{/if}
 
 		{#if type === 'bank'}
 			<div>