Add Kundennummer/Nummernkreise settings and settings dialog.

Add number & setting API endpoints, StorageManager caches, and a Settings
dialog (tabs for settings keys and number ranges) reachable from the user
menu. Show Kundennummer and creation date in the Kunde list, and refactor
Neuer Kunde to show an auto-generated number with group select.

src/api/StorageManager.js

@@ -297,6 +297,7 @@ export class StorageManager extends ApiClient {
       this.#loadCustomergroups(),
     );
     const entityCache = createCache('GET /entity', () => this.#loadEntities());
+    const numberCache = createCache('GET /number', () => this.#loadNumbers());
     const quoteCache = createCache('GET /quote', () => this.#loadQuotes());
     const orderCache = createCache('GET /order', () => this.#loadOrders());
 
@@ -352,6 +353,11 @@ export class StorageManager extends ApiClient {
       /** Settled GET /entity list, or undefined. */
       entities: { get: () => entityCache.value },
 
+      numberPromise: { get: () => numberCache.promise },
+      updateNumber: { value: numberCache.update },
+      /** Settled GET /number list, or undefined. */
+      numbers: { get: () => numberCache.value },
+
       quotePromise: { get: () => quoteCache.promise },
       updateQuote: { value: quoteCache.update },
       /** Settled GET /quote list, or undefined. */
@@ -506,6 +512,12 @@ export class StorageManager extends ApiClient {
     return requireArray(data.entities, 'entities');
   }
 
+  async #loadNumbers() {
+    const data = await this.number.list();
+    requireObject(data, 'GET /api/number');
+    return requireArray(data.numbers, 'numbers');
+  }
+
   async #loadQuotes() {
     const data = await this.quote.list();
     requireObject(data, 'GET /api/quote');