feat(mcp): Archivierte Einträge wiederherstellen und Kontostände abfragen

- archive.entities.list / archive.entities.restore für alle per MCP archivierbaren Entitäten mit Berechtigungsprüfung je Entität und Historieneintrag
- accounting.bank_accounts.balances liefert Stände von Bankkonten und Kassenbüchern, optional zu einem Stichtag

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/src/modules/bank-balances.service.ts

@@ -0,0 +1,71 @@
+import { FastifyInstance } from "fastify"
+import { and, eq, sql } from "drizzle-orm"
+import { bankaccounts, bankstatements } from "../../db/schema"
+
+export const CASHBOOK_BANK_ID = "fedeo-cashbook"
+
+type BalanceAccount = Pick<typeof bankaccounts.$inferSelect, "id" | "name" | "iban" | "ownerName" | "bankId" | "datevNumber" | "balance" | "expired" | "syncedAt">
+
+const roundMoney = (value: number) => Math.round(value * 100) / 100
+
+/**
+ * Bank accounts store the last synced booked balance; cashbooks store their opening balance
+ * and derive the current balance from their bookings. For a past date, bank balances are
+ * reconstructed by reverting the statements booked after that date.
+ */
+export function calculateAccountBalance(account: BalanceAccount, statementSum: number, asOf: string | null) {
+    const cashbook = account.bankId === CASHBOOK_BANK_ID
+    const stored = Number(account.balance || 0)
+    const balance = cashbook ? stored + statementSum : stored - statementSum
+    return {
+        id: account.id,
+        type: cashbook ? "cashbook" : "bank",
+        name: account.name || account.ownerName || (cashbook ? "Kassenbuch" : "Bankkonto"),
+        iban: cashbook ? null : account.iban,
+        datevNumber: account.datevNumber,
+        expired: account.expired,
+        balance: roundMoney(balance),
+        currency: "EUR",
+        ...(cashbook ? { openingBalance: roundMoney(stored) } : { syncedBalance: roundMoney(stored), syncedAt: account.syncedAt }),
+        source: cashbook ? "cashbook_bookings" : asOf ? "bank_sync_reconstructed" : "bank_sync",
+    }
+}
+
+export async function loadBankBalances(server: FastifyInstance, tenantId: number, options: { account?: number | null; asOf?: string | null } = {}) {
+    const asOf = options.asOf || null
+    const conditions = [eq(bankaccounts.tenant, tenantId), eq(bankaccounts.archived, false)]
+    if (options.account) conditions.push(eq(bankaccounts.id, options.account))
+    const accounts = await server.db.select().from(bankaccounts).where(and(...conditions)).orderBy(bankaccounts.name, bankaccounts.id)
+
+    const sums = async (dateCondition: any) => {
+        const rows = await server.db
+            .select({ account: bankstatements.account, total: sql<string>`coalesce(sum(${bankstatements.amount}), 0)` })
+            .from(bankstatements)
+            .where(and(eq(bankstatements.tenant, tenantId), eq(bankstatements.archived, false), ...(dateCondition ? [dateCondition] : [])))
+            .groupBy(bankstatements.account)
+        return new Map(rows.map((row) => [row.account, Number(row.total)]))
+    }
+    // Synced statements may carry a full timestamp; compare the calendar day only.
+    const bookingDay = sql`left(${bankstatements.date}, 10)`
+    // Cashbooks need bookings up to the date, bank accounts only those after it.
+    const cashbookSums = await sums(asOf ? sql`${bookingDay} <= ${asOf}` : null)
+    const bankSums = asOf ? await sums(sql`${bookingDay} > ${asOf}`) : new Map<number, number>()
+
+    const balances = accounts.map((account) => calculateAccountBalance(
+        account,
+        (account.bankId === CASHBOOK_BANK_ID ? cashbookSums : bankSums).get(account.id) || 0,
+        asOf,
+    ))
+    const active = balances.filter((account) => !account.expired)
+    return {
+        asOf,
+        accounts: balances,
+        totals: {
+            balance: roundMoney(active.reduce((sum, account) => sum + account.balance, 0)),
+            bank: roundMoney(active.filter((account) => account.type === "bank").reduce((sum, account) => sum + account.balance, 0)),
+            cashbook: roundMoney(active.filter((account) => account.type === "cashbook").reduce((sum, account) => sum + account.balance, 0)),
+            currency: "EUR",
+            note: "Summen ohne abgelaufene Bankverbindungen.",
+        },
+    }
+}