fix: use package.name for theme.id (#8965)

Prevents cases like #8953

src/meta/themes.js

@@ -25,9 +25,16 @@ Themes.get = async () => {
 	themes = _.flatten(themes).filter(Boolean);
 	themes = await Promise.all(themes.map(async (theme) => {
 		const config = path.join(themePath, theme, 'theme.json');
+		const pack = path.join(themePath, theme, 'package.json');
 		try {
-			const file = await fs.promises.readFile(config, 'utf8');
+			const [configFile, packageFile] = await Promise.all([
-			const configObj = JSON.parse(file);
+				fs.promises.readFile(config, 'utf8'),
+				fs.promises.readFile(pack, 'utf8'),
+			]);
+			const configObj = JSON.parse(configFile);
+			const packageObj = JSON.parse(packageFile);
+
+			configObj.id = packageObj.name;
 
 			// Minor adjustments for API output
 			configObj.type = 'local';