feat: MVP 3D-Druck Kostenkalkulator

- Single-Page HTML-App mit allen 18 Eingabefeldern
- 12 Berechnungen live (calc.js, reine Funktionen)
- LocalStorage-Persistenz, Mehrfach-Projekte via Sidebar
- Excel Im-/Export ueber SheetJS (vendored, MIT)
- Drag&Drop + File-Picker-Import
- Apple-Swiss-Styling, responsive
- Vorlagen-Excel mit 3 Reitern (Eingabe/Kalkulation/Angebot), Formeln referenzieren Eingabe
- openpyxl-Script fuer reproduzierbaren Template-Build
- 5 Test-Szenarien validiert

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

assets/state.js

@@ -0,0 +1,64 @@
+/* LocalStorage State-Management + Mehrfach-Projekte */
+/* global window */
+
+const STORAGE_KEY = 'kalk3d_projects_v1';
+const CURRENT_KEY = 'kalk3d_current_v1';
+
+const FIELDS = [
+  'projectName', 'customer', 'materialType',
+  'materialCostPerKg', 'materialUsageG',
+  'printTimeH', 'machineRate', 'powerKwh', 'powerPrice',
+  'postMin', 'postRate',
+  'packagingCost', 'shippingCost', 'setupCost',
+  'scrapPct', 'marginPct', 'quantity', 'individualAdjustment',
+  'vatPct', 'notes',
+];
+
+const makeDefault = (name = 'Neues Projekt') => ({
+  id: 'p_' + Date.now() + '_' + Math.random().toString(36).slice(2, 7),
+  projectName: name,
+  customer: '',
+  materialType: 'PLA',
+  materialCostPerKg: 25,
+  materialUsageG: 0,
+  printTimeH: 0,
+  machineRate: 3,
+  powerKwh: 0.15,
+  powerPrice: 0.35,
+  postMin: 0,
+  postRate: 30,
+  packagingCost: 0,
+  shippingCost: 0,
+  setupCost: 0,
+  scrapPct: 5,
+  marginPct: 30,
+  quantity: 1,
+  individualAdjustment: 0,
+  vatPct: 19,
+  notes: '',
+  createdAt: new Date().toISOString(),
+  updatedAt: new Date().toISOString(),
+});
+
+const load = () => {
+  try {
+    const raw = localStorage.getItem(STORAGE_KEY);
+    if (!raw) return [];
+    const parsed = JSON.parse(raw);
+    return Array.isArray(parsed) ? parsed : [];
+  } catch (e) {
+    console.warn('State-Load-Fehler:', e);
+    return [];
+  }
+};
+
+const save = (projects) => {
+  localStorage.setItem(STORAGE_KEY, JSON.stringify(projects));
+};
+
+const getCurrentId = () => localStorage.getItem(CURRENT_KEY);
+const setCurrentId = (id) => localStorage.setItem(CURRENT_KEY, id);
+
+window.Store = {
+  FIELDS, makeDefault, load, save, getCurrentId, setCurrentId, STORAGE_KEY, CURRENT_KEY,
+};