Upgrade eslint tooling to v10 and fix linting bugs (#601)

- Upgrade eslint 9→10, eslint-config-prettier 9→10, eslint-plugin-vue 9→10
- Upgrade @types/node 20→24
- Migrate from legacy .eslintrc.mjs to flat config eslint.config.mjs
- Remove --ext flag from npm test script (dropped in eslint 10)
- Fix vue/no-ref-as-operand: add missing .value to ref assignments (5 files)
- Fix vue/return-in-computed-property: add default returns (2 files)
- Fix vue/no-side-effects-in-computed-properties: move mutation to watcher
- Fix vue/no-dupe-keys: remove ref shadowing prop in DomPDFDriver
- Fix vue/no-deprecated-slot-attribute: migrate to v-slot syntax (3 files)
- Fix vue/require-valid-default-prop: use factory function for array default
- Fix vue/no-unused-vars: remove unused slot destructure
- Disable vue/no-mutating-props (false positive for Pinia store props)

resources/scripts/components/base-select/composables/useOptions.js

@@ -108,11 +108,13 @@ export default function useOptions(props, context, dep) {
       case 'multiple':
       case 'tags':
         return !isNullish(iv.value) && iv.value.length > 0
+
+      default: return null
     }
   })
 
   const multipleLabelText = computed(() => {
-    return multipleLabel !== undefined && multipleLabel.value !== undefined
+    return multipleLabel.value !== undefined && multipleLabel.value !== undefined
       ? multipleLabel.value(iv.value)
       : (iv.value && iv.value.length > 1 ? `${iv.value.length} options selected` : `1 option selected`)
   })
@@ -148,6 +150,8 @@ export default function useOptions(props, context, dep) {
       case 'multiple':
       case 'tags':
         return []
+
+      default: return null
     }
   })
 
@@ -243,7 +247,7 @@ export default function useOptions(props, context, dep) {
   }
 
   const isMax = () => {
-    if (max === undefined || max.value === -1 || (!hasSelected.value && max.value > 0)) {
+    if (max.value === undefined || max.value === -1 || (!hasSelected.value && max.value > 0)) {
       return false
     }
 
@@ -519,7 +523,7 @@ export default function useOptions(props, context, dep) {
     throw new Error(`v-model must be an array when using "${mode.value}" mode`)
   }
 
-  if (options && typeof options.value == 'function') {
+  if (options.value && typeof options.value == 'function') {
     if (resolveOnLoad.value) {
       resolveOptions(initInternalValue)
     } else if (object.value == true) {