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>

.prettierrc

@@ -0,0 +1,10 @@
+{
+  "singleQuote": true,
+  "trailingComma": "all",
+  "tabWidth": 2,
+  "semi": true,
+  "printWidth": 100,
+  "bracketSpacing": true,
+  "arrowParens": "always",
+  "endOfLine": "lf"
+}