Add full application: receipt scanning, auth, billing, and account deletion

Brings the working codebase (Next.js app, auth system, Stripe billing,
Docker/deploy config, tests, docs) into version control on top of the
placeholder initial commit, and adds account self-deletion (Danger Zone
in Settings, password + typed-email confirmation, cascading DB cleanup,
Stripe cancellation) per GDPR right-to-erasure.

Excludes local build caches, node_modules, and internal agent scratch
files; .gitignore hardened to keep those out going forward.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

scripts/inspect_excel.mjs

@@ -0,0 +1,29 @@
+import ExcelJS from "exceljs";
+
+async function inspect() {
+  const wb = new ExcelJS.Workbook();
+  await wb.xlsx.readFile("C:/Users/timo/Downloads/Belege_Export_2026-08-14.xlsx");
+
+  console.log("=== WORKBOOK SHEETS ===");
+  wb.eachSheet((sheet, id) => {
+    console.log(`Sheet ${id}: "${sheet.name}" (Rows: ${sheet.rowCount}, Cols: ${sheet.columnCount})`);
+  });
+
+  const s1 = wb.getWorksheet("Belegübersicht");
+  if (s1) {
+    console.log("\n=== SHEET 1: Belegübersicht ===");
+    s1.eachRow((row, rowNumber) => {
+      console.log(`Row ${rowNumber}:`, JSON.stringify(row.values));
+    });
+  }
+
+  const s2 = wb.getWorksheet("Einzelpositionen Detail");
+  if (s2) {
+    console.log("\n=== SHEET 2: Einzelpositionen Detail ===");
+    s2.eachRow((row, rowNumber) => {
+      console.log(`Row ${rowNumber}:`, JSON.stringify(row.values));
+    });
+  }
+}
+
+inspect().catch(console.error);