feat: initialize monorepo structure with Bun and Turborepo

- Add package.json for the root with workspace configuration and scripts
- Create @gruperly/config package with TypeScript configuration
- Establish shared package @gruperly/shared with Zod schemas for validation
- Implement group, student, and payment schemas using Zod
- Set up TypeScript configuration for shared package
- Document stack architecture and technical specifications in stack.md
- Configure Turborepo with build, dev, lint, and typecheck tasks

apps/api/tsconfig.json

@@ -0,0 +1,11 @@
+{
+  "extends": "@gruperly/config/tsconfig.base.json",
+  "compilerOptions": {
+    "moduleResolution": "bundler",
+    "types": ["bun"],
+    "paths": {
+      "@gruperly/shared": ["../../packages/shared/src/index.ts"]
+    }
+  },
+  "include": ["src/**/*.ts"]
+}