refactor(frontend): Formまわりの型強化 (#16260)

* refactor(frontend): Formまわりの型強化

* fix

* avoid non-null assertion and add null check for safety

* refactor

* avoid non-null assertion and add null check for safety

* Update clip.vue

---------

Co-authored-by: syuilo <4439005+syuilo@users.noreply.github.com>

packages/frontend/src/widgets/WidgetAiscriptApp.vue

@@ -18,7 +18,7 @@ import type { Ref } from 'vue';
 import { Interpreter, Parser } from '@syuilo/aiscript';
 import { useWidgetPropsManager } from './widget.js';
 import type { WidgetComponentEmits, WidgetComponentExpose, WidgetComponentProps } from './widget.js';
-import type { GetFormResultType } from '@/utility/form.js';
+import type { FormWithDefault, GetFormResultType } from '@/utility/form.js';
 import * as os from '@/os.js';
 import { aiScriptReadline, createAiScriptEnv } from '@/aiscript/api.js';
 import { $i } from '@/i.js';
@@ -31,15 +31,15 @@ const name = 'aiscriptApp';
 
 const widgetPropsDef = {
 	script: {
-		type: 'string' as const,
+		type: 'string',
 		multiline: true,
 		default: '',
 	},
 	showHeader: {
-		type: 'boolean' as const,
+		type: 'boolean',
 		default: true,
 	},
-};
+} satisfies FormWithDefault;
 
 type WidgetProps = GetFormResultType<typeof widgetPropsDef>;
 
@@ -92,7 +92,7 @@ async function run() {
 		os.alert({
 			type: 'error',
 			title: 'AiScript Error',
-			text: err.message,
+			text: err instanceof Error ? err.message : String(err),
 		});
 	}
 }