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/test_gpt5.mjs

@@ -0,0 +1,39 @@
+import fs from "fs";
+import { generateObject } from "ai";
+import { createOpenAI } from "@ai-sdk/openai";
+import { ReceiptExtractionSchema } from "../src/lib/schema/receipt.ts";
+
+const envContent = fs.readFileSync(".env.local", "utf-8");
+const apiKeyMatch = envContent.match(/OPENROUTER_API_KEY=([^\r\n]+)/);
+const apiKey = apiKeyMatch ? apiKeyMatch[1].trim() : "";
+
+const demoImgPath = "public/demo/01_aral_tankbeleg_muenchen.jpg";
+const imgBase64 = fs.readFileSync(demoImgPath).toString("base64");
+const dataUrl = `data:image/jpeg;base64,${imgBase64}`;
+
+async function testGpt5Models() {
+  const models = ["openai/gpt-5-mini", "openai/gpt-5.4-mini", "openai/gpt-4o-mini"];
+  const openrouter = createOpenAI({
+    apiKey,
+    baseURL: "https://openrouter.ai/api/v1",
+  });
+
+  for (const m of models) {
+    console.log(`\nTesting ${m}...`);
+    try {
+      const { object } = await generateObject({
+        model: openrouter(m),
+        schema: ReceiptExtractionSchema,
+        messages: [
+          { role: "system", content: "Extrahiere den Beleg." },
+          { role: "user", content: [{ type: "text", text: "Beleg:" }, { type: "image", image: dataUrl }] },
+        ],
+      });
+      console.log(`✓ SUCCESS with ${m}! Merchant: ${object.merchant.name}, Total: ${object.totalAmount.value}`);
+    } catch (err) {
+      console.log(`✗ Error with ${m}:`, err.message);
+    }
+  }
+}
+
+testGpt5Models().catch(console.error);