feat: add ESLint flat config, Prettier, dependency-cruiser, and Husky

Setup code quality tooling for the monorepo:
- ESLint 9 flat config with TypeScript, import ordering, and NestJS rules
- Prettier with consistent formatting across all files
- dependency-cruiser enforcing module boundary rules (no cross-module internals, no circular deps)
- Husky + lint-staged for pre-commit hooks
- Auto-fixed existing files for type imports and import ordering

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/tsconfig.json

@@ -8,8 +8,11 @@
     "emitDecoratorMetadata": true,
     "experimentalDecorators": true,
     "declaration": false,
-    "declarationMap": false
+    "declarationMap": false,
+    "paths": {
+      "@modules/*": ["../../src/modules/*"]
+    }
   },
-  "include": ["src/**/*"],
+  "include": ["src/**/*", "../../src/modules/**/*"],
   "exclude": ["node_modules", "dist"]
 }