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/tsconfig-paths-loader.mjs

@@ -0,0 +1,7 @@
+/**
+ * Loader entry: registers the path-alias hooks module for the current process.
+ * Usage:  node --import ./tests/integration/tsconfig-paths-loader.mjs tests/integration/<suite>.test.ts
+ */
+import { register } from "node:module";
+
+register(new URL("./tsconfig-paths-hooks.mjs", import.meta.url));