feat: integer cents money handling, order page fixes, and vendor filter persistence

Money Handling Architecture:
- Store all monetary values as integer cents (€105.91 = 10591)
- Add app/utils/money.py with Money class and conversion helpers
- Add static/shared/js/money.js for frontend formatting
- Update all database models to use _cents columns (Product, Order, etc.)
- Update CSV processor to convert prices to cents on import
- Add Alembic migration for Float to Integer conversion
- Create .architecture-rules/money.yaml with 7 validation rules
- Add docs/architecture/money-handling.md documentation

Order Details Page Fixes:
- Fix customer name showing 'undefined undefined' - use flat field names
- Fix vendor info empty - add vendor_name/vendor_code to OrderDetailResponse
- Fix shipping address using wrong nested object structure
- Enrich order detail API response with vendor info

Vendor Filter Persistence Fixes:
- Fix orders.js: restoreSavedVendor now sets selectedVendor and filters
- Fix orders.js: init() only loads orders if no saved vendor to restore
- Fix marketplace-letzshop.js: restoreSavedVendor calls selectVendor()
- Fix marketplace-letzshop.js: clearVendorSelection clears TomSelect dropdown
- Align vendor selector placeholder text between pages

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/shared/js/money.js

@@ -0,0 +1,193 @@
+// static/shared/js/money.js
+/**
+ * Money handling utilities using integer cents.
+ *
+ * All monetary values are stored as integers representing cents in the database.
+ * The API returns euros (converted from cents on the backend), but these utilities
+ * can be used if cents are passed to the frontend.
+ *
+ * Example:
+ *     105.91 EUR is stored as 10591 (integer cents)
+ *
+ * Usage:
+ *     Money.format(10591)                    // Returns "105.91"
+ *     Money.format(10591, 'EUR')             // Returns "105,91 EUR"
+ *     Money.toCents(105.91)                  // Returns 10591
+ *     Money.toEuros(10591)                   // Returns 105.91
+ *     Money.formatEuros(105.91, 'EUR')       // Returns "105,91 EUR"
+ *
+ * See docs/architecture/money-handling.md for full documentation.
+ */
+
+const Money = {
+    /**
+     * Format cents as a currency string.
+     *
+     * @param {number} cents - Amount in cents
+     * @param {string} currency - Currency code (default: '', no currency shown)
+     * @param {string} locale - Locale for formatting (default: 'de-DE')
+     * @returns {string} Formatted price string
+     *
+     * @example
+     * Money.format(10591)           // "105.91"
+     * Money.format(10591, 'EUR')    // "105,91 EUR" (German locale)
+     * Money.format(1999)            // "19.99"
+     */
+    format(cents, currency = '', locale = 'de-DE') {
+        if (cents === null || cents === undefined) {
+            cents = 0;
+        }
+
+        const euros = cents / 100;
+
+        if (currency) {
+            return new Intl.NumberFormat(locale, {
+                style: 'currency',
+                currency: currency
+            }).format(euros);
+        }
+
+        return new Intl.NumberFormat(locale, {
+            minimumFractionDigits: 2,
+            maximumFractionDigits: 2
+        }).format(euros);
+    },
+
+    /**
+     * Convert euros to cents.
+     *
+     * @param {number|string} euros - Amount in euros
+     * @returns {number} Amount in cents (integer)
+     *
+     * @example
+     * Money.toCents(105.91)    // 10591
+     * Money.toCents('19.99')   // 1999
+     * Money.toCents(null)      // 0
+     */
+    toCents(euros) {
+        if (euros === null || euros === undefined || euros === '') {
+            return 0;
+        }
+        return Math.round(parseFloat(euros) * 100);
+    },
+
+    /**
+     * Convert cents to euros.
+     *
+     * @param {number} cents - Amount in cents
+     * @returns {number} Amount in euros
+     *
+     * @example
+     * Money.toEuros(10591)    // 105.91
+     * Money.toEuros(1999)     // 19.99
+     * Money.toEuros(null)     // 0
+     */
+    toEuros(cents) {
+        if (cents === null || cents === undefined) {
+            return 0;
+        }
+        return cents / 100;
+    },
+
+    /**
+     * Format a euro amount for display.
+     *
+     * Use this when the value is already in euros (e.g., from API response).
+     *
+     * @param {number} euros - Amount in euros
+     * @param {string} currency - Currency code (default: 'EUR')
+     * @param {string} locale - Locale for formatting (default: 'de-DE')
+     * @returns {string} Formatted price string
+     *
+     * @example
+     * Money.formatEuros(105.91, 'EUR')    // "105,91 EUR"
+     * Money.formatEuros(19.99)            // "19.99"
+     */
+    formatEuros(euros, currency = '', locale = 'de-DE') {
+        if (euros === null || euros === undefined) {
+            euros = 0;
+        }
+
+        if (currency) {
+            return new Intl.NumberFormat(locale, {
+                style: 'currency',
+                currency: currency
+            }).format(euros);
+        }
+
+        return new Intl.NumberFormat(locale, {
+            minimumFractionDigits: 2,
+            maximumFractionDigits: 2
+        }).format(euros);
+    },
+
+    /**
+     * Parse a price string to cents.
+     *
+     * Handles various formats:
+     * - "19.99 EUR"
+     * - "19,99"
+     * - 19.99
+     *
+     * @param {string|number} priceStr - Price string or number
+     * @returns {number} Amount in cents
+     *
+     * @example
+     * Money.parse("19.99 EUR")    // 1999
+     * Money.parse("19,99")        // 1999
+     * Money.parse(19.99)          // 1999
+     */
+    parse(priceStr) {
+        if (priceStr === null || priceStr === undefined || priceStr === '') {
+            return 0;
+        }
+
+        if (typeof priceStr === 'number') {
+            return Math.round(priceStr * 100);
+        }
+
+        // Remove currency symbols and spaces
+        let cleaned = priceStr.toString().replace(/[^\d,.-]/g, '');
+
+        // Handle European decimal comma
+        cleaned = cleaned.replace(',', '.');
+
+        try {
+            return Math.round(parseFloat(cleaned) * 100);
+        } catch {
+            return 0;
+        }
+    },
+
+    /**
+     * Calculate line total (unit price * quantity).
+     *
+     * @param {number} unitPriceCents - Price per unit in cents
+     * @param {number} quantity - Number of units
+     * @returns {number} Total in cents
+     */
+    calculateLineTotal(unitPriceCents, quantity) {
+        return unitPriceCents * quantity;
+    },
+
+    /**
+     * Calculate order total.
+     *
+     * @param {number} subtotalCents - Sum of line items in cents
+     * @param {number} taxCents - Tax amount in cents (default: 0)
+     * @param {number} shippingCents - Shipping cost in cents (default: 0)
+     * @param {number} discountCents - Discount amount in cents (default: 0)
+     * @returns {number} Total in cents
+     */
+    calculateOrderTotal(subtotalCents, taxCents = 0, shippingCents = 0, discountCents = 0) {
+        return subtotalCents + taxCents + shippingCents - discountCents;
+    }
+};
+
+// Make available globally
+window.Money = Money;
+
+// Export for modules
+if (typeof module !== 'undefined' && module.exports) {
+    module.exports = Money;
+}