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/integration/loadEnv.ts

@@ -0,0 +1,36 @@
+/**
+ * Loads `.env.local` as a side effect on import.
+ *
+ * This has to be its own module: ES module imports are hoisted, so calling
+ * `process.loadEnvFile()` at the top of a file that also imports the database
+ * module would run *after* that module had already read `DATABASE_URL`. Imported
+ * first, this module is evaluated first.
+ *
+ * It matters because the fallback connection string targets port 5432, which on
+ * a development machine is quite likely another project's database.
+ */
+try {
+  process.loadEnvFile(".env.local");
+} catch {
+  // No .env.local (CI, fresh clone): use the environment as given.
+}
+
+/**
+ * Hard guarantee that the suite never sends mail.
+ *
+ * The fixtures operate on fabricated addresses (`authtest-…@gmail.com`), and a
+ * configured SMTP server would dutifully try to deliver to them — bouncing off
+ * real providers and burning the sending domain's reputation. Clearing these
+ * puts the mailer into its development fallback, which returns the link instead
+ * of sending it, which is also how the tests get hold of the raw token.
+ */
+delete process.env.SMTP_HOST;
+delete process.env.SMTP_USER;
+delete process.env.SMTP_PASSWORD;
+
+// The dev fallback throws in production rather than silently not sending.
+if (process.env.NODE_ENV === "production") {
+  throw new Error("Refusing to run the auth integration suite with NODE_ENV=production");
+}
+
+export {};