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>

eslint.config.mjs

@@ -0,0 +1,121 @@
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import importPlugin from 'eslint-plugin-import-x';
+import eslintConfigPrettier from 'eslint-config-prettier';
+import globals from 'globals';
+
+export default tseslint.config(
+  // Global ignores
+  {
+    ignores: [
+      '**/node_modules/**',
+      '**/dist/**',
+      '**/.next/**',
+      '**/coverage/**',
+      '**/*.js',
+      '**/*.cjs',
+      '**/*.mjs',
+      '!eslint.config.mjs',
+    ],
+  },
+
+  // Base JS recommended rules
+  js.configs.recommended,
+
+  // TypeScript recommended rules
+  ...tseslint.configs.recommended,
+
+  // Import plugin
+  importPlugin.flatConfigs.recommended,
+  importPlugin.flatConfigs.typescript,
+
+  // Prettier (disables conflicting rules)
+  eslintConfigPrettier,
+
+  // Shared settings for all TS files
+  {
+    files: ['**/*.ts', '**/*.tsx'],
+    languageOptions: {
+      globals: {
+        ...globals.node,
+      },
+    },
+    settings: {
+      'import-x/resolver': {
+        typescript: {
+          project: ['apps/*/tsconfig.json', 'tsconfig.base.json'],
+        },
+      },
+    },
+    rules: {
+      // TypeScript
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        { argsIgnorePattern: '^_', varsIgnorePattern: '^_' },
+      ],
+      '@typescript-eslint/no-explicit-any': 'warn',
+      '@typescript-eslint/consistent-type-imports': [
+        'error',
+        { prefer: 'type-imports', fixStyle: 'inline-type-imports' },
+      ],
+
+      // Import ordering
+      'import-x/order': [
+        'error',
+        {
+          groups: ['builtin', 'external', 'internal', 'parent', 'sibling', 'index'],
+          'newlines-between': 'never',
+          alphabetize: { order: 'asc', caseInsensitive: true },
+        },
+      ],
+      'import-x/no-duplicates': 'error',
+      'import-x/no-unresolved': 'off', // TypeScript handles this
+
+      // General
+      'no-console': ['warn', { allow: ['warn', 'error'] }],
+    },
+  },
+
+  // NestJS-specific rules for the API app
+  {
+    files: ['apps/api/**/*.ts', 'src/modules/**/*.ts'],
+    rules: {
+      // NestJS uses empty classes for modules, allow them
+      '@typescript-eslint/no-extraneous-class': 'off',
+      // NestJS decorators require this pattern
+      '@typescript-eslint/no-unsafe-declaration-merging': 'off',
+    },
+  },
+
+  // React/Next.js overrides for web app
+  {
+    files: ['apps/web/**/*.ts', 'apps/web/**/*.tsx'],
+    languageOptions: {
+      globals: {
+        ...globals.browser,
+        React: 'readonly',
+      },
+    },
+    rules: {
+      'no-console': 'error',
+    },
+  },
+
+  // Test files
+  {
+    files: ['**/*.spec.ts', '**/*.test.ts', '**/__tests__/**/*.ts'],
+    rules: {
+      '@typescript-eslint/no-explicit-any': 'off',
+      'no-console': 'off',
+    },
+  },
+
+  // Script files (seeds, migrations, etc.)
+  {
+    files: ['prisma/**/*.ts'],
+    rules: {
+      'no-console': 'off',
+      '@typescript-eslint/no-unused-vars': 'warn',
+    },
+  },
+);