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>

src/app/api/subscription/cancel/route.ts

@@ -0,0 +1,98 @@
+import { NextRequest, NextResponse } from "next/server";
+import Stripe from "stripe";
+import { eq } from "drizzle-orm";
+import { getCurrentUser } from "@/lib/auth/session";
+import { requireCsrf } from "@/lib/auth/csrf";
+import { db, isDatabaseAvailable, schema } from "@/lib/db";
+
+const stripe = process.env.STRIPE_SECRET_KEY
+  ? new Stripe(process.env.STRIPE_SECRET_KEY, {
+      apiVersion: "2025-01-27.acacia" as any,
+      maxNetworkRetries: 2,
+    })
+  : null;
+
+export const runtime = "nodejs";
+
+export async function POST(req: NextRequest) {
+  try {
+    const csrfBlocked = requireCsrf(req);
+    if (csrfBlocked) return csrfBlocked;
+
+    const user = await getCurrentUser();
+    if (!user) {
+      return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+    }
+
+    const hasDb = await isDatabaseAvailable().catch(() => false);
+
+    // A recurring Stripe subscription is cancelled at period end, so Pro
+    // access (and the Pro badge) continues for whatever the user already
+    // paid for. A plan with no subscription behind it (lifetime, or a plan
+    // granted without Stripe) has no period to run out, so it downgrades
+    // immediately instead.
+    if (user.stripeSubscriptionId && stripe) {
+      try {
+        await stripe.subscriptions.update(user.stripeSubscriptionId, {
+          cancel_at_period_end: true,
+        });
+      } catch (stripeErr: any) {
+        console.warn("Could not schedule Stripe subscription cancellation (may already be cancelled):", stripeErr?.message);
+      }
+
+      if (hasDb) {
+        try {
+          // Optimistic UI flag — the authoritative sync happens via the
+          // customer.subscription.updated webhook, which may lag behind.
+          await db
+            .update(schema.users)
+            .set({
+              cancelAtPeriodEnd: true,
+              updatedAt: new Date(),
+            })
+            .where(eq(schema.users.id, user.id));
+        } catch (dbErr) {
+          console.error("Database error while scheduling subscription cancellation:", dbErr);
+        }
+      }
+
+      return NextResponse.json({
+        success: true,
+        scheduled: true,
+        expiresAt: user.expiresAt ? user.expiresAt.toISOString() : null,
+        message: "Subscription will cancel at the end of the current billing period.",
+      });
+    }
+
+    // No Stripe subscription behind the plan — downgrade immediately.
+    if (hasDb) {
+      try {
+        await db
+          .update(schema.users)
+          .set({
+            plan: "free",
+            stripeSubscriptionId: null,
+            expiresAt: null,
+            cancelAtPeriodEnd: false,
+            updatedAt: new Date(),
+          })
+          .where(eq(schema.users.id, user.id));
+      } catch (dbErr) {
+        console.error("Database error while cancelling subscription:", dbErr);
+      }
+    }
+
+    return NextResponse.json({
+      success: true,
+      scheduled: false,
+      plan: "free",
+      message: "Subscription cancelled and downgraded to Free successfully.",
+    });
+  } catch (error: any) {
+    console.error("Subscription cancel error:", error);
+    return NextResponse.json(
+      { error: error?.message || "Fehler beim Kündigen des Abonnements." },
+      { status: 500 }
+    );
+  }
+}