feat : add ESLint linter to frontend with pre-commit hook

Add ESLint with @nuxt/eslint-config enforcing 4-space indentation.
Add make nuxt-lint and nuxt-lint-fix targets.
Add ESLint check to pre-commit hook (lint only, no auto-fix).
Fix auth.vue indentation from 2 to 4 spaces.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/eslint.config.mjs

@@ -0,0 +1,60 @@
+import nuxt from '@nuxt/eslint-config'
+
+export default await nuxt(
+    {
+        features: {
+            stylistic: false,
+            typescript: true,
+            nuxt: {
+                sortConfigKeys: false,
+            },
+        },
+        dirs: {
+            root: ['.', './app'],
+        },
+    },
+    {
+        name: 'coltura/custom-overrides',
+        rules: {
+            // Indentation 4 espaces (convention CLAUDE.md)
+            'vue/html-indent': ['error', 4],
+            indent: ['error', 4, { SwitchCase: 1 }],
+
+            // Vue — relaxed
+            'vue/multi-word-component-names': 'off',
+            'vue/no-multiple-template-root': 'off',
+            'vue/require-default-prop': 'off',
+            'vue/html-self-closing': 'off',
+            'vue/singleline-html-element-content-newline': 'off',
+            'vue/multiline-html-element-content-newline': 'off',
+            'vue/attributes-order': 'off',
+            'vue/v-on-event-hyphenation': 'off',
+
+            // Console — allow console.error only
+            'no-console': ['warn', { allow: ['error'] }],
+
+            // Unused vars — warn, ignore underscore-prefixed
+            'no-unused-vars': 'off',
+            '@typescript-eslint/no-unused-vars': ['warn', {
+                argsIgnorePattern: '^_',
+                varsIgnorePattern: '^_',
+                caughtErrorsIgnorePattern: '^_',
+            }],
+
+            // TypeScript — progressive strictness
+            '@typescript-eslint/no-explicit-any': 'warn',
+            '@typescript-eslint/no-dynamic-delete': 'off',
+            '@typescript-eslint/no-invalid-void-type': 'off',
+
+            // Formatting — leave to stylistic tools
+            'require-await': 'off',
+            'comma-dangle': 'off',
+            curly: 'off',
+            semi: 'off',
+            quotes: 'off',
+            'no-trailing-spaces': 'off',
+            'no-multiple-empty-lines': 'off',
+            'no-irregular-whitespace': 'off',
+        },
+    },
+)