chore(lint): enable strict ESLint rules and fix unused-vars violations (F4.1)

Enable no-console (warn, allow error), @typescript-eslint/no-unused-vars
(warn, ignore _ prefix), and @typescript-eslint/no-explicit-any (warn).
Fix all 26 no-unused-vars violations across 9 files.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

eslint.config.mjs

@@ -9,6 +9,7 @@ const globals = {
 };
 
 const relaxedRules = {
+  // Vue rules — relaxed for legacy code
   'vue/no-parsing-error': 'off',
   'vue/no-required-prop-with-default': 'off',
   'vue/no-mutating-props': 'off',
@@ -21,8 +22,25 @@ const relaxedRules = {
   'vue/no-multiple-template-root': 'off',
   'vue/v-on-event-hyphenation': 'off',
   'vue/require-default-prop': 'off',
-  'no-console': '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',
+  '@typescript-eslint/unified-signatures': 'off',
+
+  // Formatting — handled by Prettier/stylistic
   'require-await': 'off',
   'comma-dangle': 'off',
   curly: 'off',
@@ -30,6 +48,7 @@ const relaxedRules = {
   'space-before-function-paren': 'off',
   'arrow-parens': 'off',
   semi: 'off',
+  '@typescript-eslint/semi': 'off',
   quotes: 'off',
   'func-call-spacing': 'off',
   'no-trailing-spaces': 'off',
@@ -39,12 +58,6 @@ const relaxedRules = {
   'no-irregular-whitespace': 'off',
   'no-useless-escape': 'off',
   'nuxt/prefer-import-meta': 'off',
-  '@typescript-eslint/no-unused-vars': 'off',
-  '@typescript-eslint/semi': 'off',
-  '@typescript-eslint/no-explicit-any': 'off',
-  '@typescript-eslint/no-dynamic-delete': 'off',
-  '@typescript-eslint/no-invalid-void-type': 'off',
-  '@typescript-eslint/unified-signatures': 'off',
 };
 
 export default await nuxt(