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>

tests/e2e/seo_slugs.test.ts

@@ -0,0 +1,89 @@
+/**
+ * Locale-specific SEO slugs — public German keyword URLs rewrite onto the
+ * shared App Router folders; English slugs under /de/ 301 to the DE slug.
+ */
+
+import { describe, test, expect } from "./runner";
+import {
+  decideSeoLocalePath,
+  localizePathname,
+  publicPath,
+} from "../../src/lib/seo/slugs";
+
+describe("SEO slugs — public paths", () => {
+  test("German blog slugs use keyword URLs", () => {
+    expect(publicPath("de", "blog/simple-expense-tracking")).toBe(
+      "/de/blog/einfache-ausgabenverfolgung",
+    );
+    expect(publicPath("en", "blog/simple-expense-tracking")).toBe(
+      "/en/blog/simple-expense-tracking",
+    );
+  });
+
+  test("German keyword pages use German slugs", () => {
+    expect(publicPath("de", "ocr-receipt-scanner")).toBe("/de/beleg-ocr");
+    expect(publicPath("de", "expense-tracker-freelancers")).toBe(
+      "/de/ausgaben-tracker-freelancer",
+    );
+    expect(publicPath("de", "expensify-alternative")).toBe("/de/alternative-zu-expensify");
+    expect(publicPath("de", "lexoffice-alternative")).toBe("/de/alternative-zu-lexoffice");
+  });
+});
+
+describe("SEO slugs — middleware decisions", () => {
+  test("DE public slug rewrites onto the internal folder", () => {
+    expect(decideSeoLocalePath("/de/blog/einfache-ausgabenverfolgung")).toEqual({
+      kind: "rewrite",
+      pathname: "/de/blog/simple-expense-tracking",
+    });
+    expect(decideSeoLocalePath("/de/beleg-ocr")).toEqual({
+      kind: "rewrite",
+      pathname: "/de/ocr-receipt-scanner",
+    });
+  });
+
+  test("English slug under /de/ redirects to the German keyword URL", () => {
+    expect(decideSeoLocalePath("/de/blog/simple-expense-tracking")).toEqual({
+      kind: "redirect",
+      pathname: "/de/blog/einfache-ausgabenverfolgung",
+    });
+    expect(decideSeoLocalePath("/de/ocr-receipt-scanner")).toEqual({
+      kind: "redirect",
+      pathname: "/de/beleg-ocr",
+    });
+  });
+
+  test("German slug under /en/ redirects to the English URL", () => {
+    expect(decideSeoLocalePath("/en/blog/einfache-ausgabenverfolgung")).toEqual({
+      kind: "redirect",
+      pathname: "/en/blog/simple-expense-tracking",
+    });
+  });
+
+  test("correct English public slugs pass through", () => {
+    expect(decideSeoLocalePath("/en/blog/simple-expense-tracking")).toEqual({
+      kind: "none",
+    });
+    expect(decideSeoLocalePath("/en/ocr-receipt-scanner")).toEqual({ kind: "none" });
+  });
+
+  test("homepage and blog index are untouched", () => {
+    expect(decideSeoLocalePath("/de")).toEqual({ kind: "none" });
+    expect(decideSeoLocalePath("/en")).toEqual({ kind: "none" });
+    expect(decideSeoLocalePath("/de/blog")).toEqual({ kind: "none" });
+    expect(decideSeoLocalePath("/en/blog")).toEqual({ kind: "none" });
+  });
+});
+
+describe("SEO slugs — language switch", () => {
+  test("maps the sibling locale slug instead of only swapping /en and /de", () => {
+    expect(localizePathname("/en/blog/simple-expense-tracking", "de")).toBe(
+      "/de/blog/einfache-ausgabenverfolgung",
+    );
+    expect(localizePathname("/de/blog/einfache-ausgabenverfolgung", "en")).toBe(
+      "/en/blog/simple-expense-tracking",
+    );
+    expect(localizePathname("/de", "en")).toBe("/en");
+    expect(localizePathname("/en/blog", "de")).toBe("/de/blog");
+  });
+});