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>

.dependency-cruiser.cjs

@@ -0,0 +1,79 @@
+/** @type {import('dependency-cruiser').IConfiguration} */
+module.exports = {
+  forbidden: [
+    // No circular dependencies
+    {
+      name: 'no-circular',
+      severity: 'error',
+      comment: 'Circular dependencies are not allowed.',
+      from: {},
+      to: { circular: true },
+    },
+
+    // Modules must not import internals of other modules directly.
+    // Only import via the module's public barrel (index.ts).
+    {
+      name: 'no-cross-module-internals',
+      severity: 'error',
+      comment:
+        'Modules must not import internal files of other modules. Import from the module index (barrel) instead.',
+      from: {
+        path: 'src/modules/([^/]+)/',
+      },
+      to: {
+        path: 'src/modules/([^/]+)/.+',
+        pathNot: [
+          // Allow importing from the module's own files
+          'src/modules/$1/',
+          // Allow importing from another module's barrel index
+          'src/modules/[^/]+/index\\.ts$',
+        ],
+      },
+    },
+
+    // Apps should not import module internals either
+    {
+      name: 'no-app-to-module-internals',
+      severity: 'error',
+      comment: 'Apps must import modules via their barrel index, not internal files.',
+      from: {
+        path: 'apps/',
+      },
+      to: {
+        path: 'src/modules/([^/]+)/.+',
+        pathNot: ['src/modules/[^/]+/index\\.ts$'],
+      },
+    },
+
+    // No orphan modules (files not reachable from any entry point)
+    {
+      name: 'no-orphans',
+      severity: 'warn',
+      comment: 'Orphan modules may indicate dead code.',
+      from: {
+        orphan: true,
+        pathNot: ['\\.(spec|test)\\.ts$', '__tests__/', '\\.d\\.ts$', 'index\\.ts$'],
+      },
+      to: {},
+    },
+  ],
+
+  options: {
+    doNotFollow: {
+      path: ['node_modules', '\\.next', 'dist'],
+    },
+    tsPreCompilationDeps: true,
+    tsConfig: {
+      fileName: 'tsconfig.base.json',
+    },
+    enhancedResolveOptions: {
+      exportsFields: ['exports'],
+      conditionNames: ['import', 'require', 'node', 'default'],
+    },
+    reporterOptions: {
+      text: {
+        highlightFocused: true,
+      },
+    },
+  },
+};