Add FX rate per account, convert foreign balances to base currency in budget

Accounts now have fxRateToBase (default 1.0). The budget total query
multiplies each transaction by the account's rate, so a USD account
with rate 34.5 contributes correctly to the THB-denominated budget.

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

src/lib/server/db/schema.ts

@@ -893,6 +893,8 @@ export const companyAccounts = pgTable(
 		creditLimit: numeric('credit_limit', { precision: 15, scale: 2 }),
 		statementCloseDay: integer('statement_close_day'),
 		paymentDueDay: integer('payment_due_day'),
+		// FX conversion to company base currency (e.g. 34.5 for USD→THB)
+		fxRateToBase: numeric('fx_rate_to_base', { precision: 18, scale: 8 }).notNull().default('1'),
 		// Banking integration link
 		externalAccountId: uuid('external_account_id').references(() => externalAccounts.id, {
 			onDelete: 'set null'

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

@@ -27,10 +27,10 @@ export const load: LayoutServerLoad = async ({ locals, params }) => {
 		error(403, 'Not a member of this company');
 	}
 
-	// Total budget = sum of all non-deleted account balances
+	// Total budget = sum of all non-deleted account balances, converted to base currency
 	const [balanceRow] = await db
 		.select({
-			total: sql<string>`coalesce(sum(${companyAccountTransactions.amount}), '0')::text`
+			total: sql<string>`coalesce(sum(${companyAccountTransactions.amount} * ${companyAccounts.fxRateToBase}), '0')::text`
 		})
 		.from(companyAccountTransactions)
 		.innerJoin(companyAccounts, eq(companyAccountTransactions.accountId, companyAccounts.id))

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

@@ -112,6 +112,7 @@ type AccountFields = {
 	creditLimit: string | null;
 	statementCloseDay: number | null;
 	paymentDueDay: number | null;
+	fxRateToBase: string;
 	externalAccountId: string | null;
 };
 
@@ -171,6 +172,7 @@ function extractAccountFields(fd: FormData):
 			creditLimit: parseDecimalOrNull(fd.get('creditLimit')),
 			statementCloseDay,
 			paymentDueDay,
+			fxRateToBase: parseDecimalOrNull(fd.get('fxRateToBase')) ?? '1',
 			externalAccountId: trimOrNull(fd.get('externalAccountId'))
 		}
 	};
@@ -304,6 +306,7 @@ export const actions: Actions = {
 					creditLimit: f.creditLimit,
 					statementCloseDay: f.statementCloseDay,
 					paymentDueDay: f.paymentDueDay,
+					fxRateToBase: f.fxRateToBase,
 					externalAccountId: f.externalAccountId
 				})
 				.returning({ id: companyAccounts.id });
@@ -383,6 +386,7 @@ export const actions: Actions = {
 				creditLimit: f.creditLimit,
 				statementCloseDay: f.statementCloseDay,
 				paymentDueDay: f.paymentDueDay,
+				fxRateToBase: f.fxRateToBase,
 				externalAccountId: f.externalAccountId,
 				updatedAt: new Date()
 			})

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

@@ -143,6 +143,7 @@
 		creditLimit?: string | null;
 		statementCloseDay?: number | null;
 		paymentDueDay?: number | null;
+		fxRateToBase?: string | null;
 		externalAccountId?: string | null;
 	} = {}
 )}
@@ -176,7 +177,20 @@
 				class={inputCls}
 			/>
 		</div>
-		<div></div>
+		<div>
+			<label for="{prefix}-fxRate" class={labelCls}>FX Rate to Base</label>
+			<input
+				id="{prefix}-fxRate"
+				name="fxRateToBase"
+				type="number"
+				step="0.0001"
+				min="0.0001"
+				value={prefill.fxRateToBase ?? '1'}
+				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>
+		</div>
 
 		{#if type === 'bank'}
 			<div>
@@ -891,6 +905,7 @@
 								creditLimit: acct.creditLimit,
 								statementCloseDay: acct.statementCloseDay,
 								paymentDueDay: acct.paymentDueDay,
+								fxRateToBase: acct.fxRateToBase,
 								externalAccountId: acct.externalAccountId
 							})}
 							<div class="mt-3 flex justify-end gap-2">