Fix kv-store load to use try/catch instead of existsSync

Replace check-then-read with read-and-catch-ENOENT. The existsSync
pattern is redundant and slightly misleading; other errors still
propagate.

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

lib/kv-store.mjs

@@ -151,12 +151,14 @@ export class Simple_KeyValue_Store {
 
 	load() {
 		const { data, storage_path } = this;
-		if (!fs.existsSync(storage_path)) {
-			return;
+		let file_contents;
+		try {
+			file_contents = fs.readFileSync(storage_path, 'utf-8');
+		} catch (e) {
+			if (e.code === 'ENOENT') { return; }
+			throw e;
 		}
 
-		const file_contents = fs.readFileSync(storage_path, 'utf-8');
-
 		for (const line of file_contents.split('\n')) {
 			if (!line) continue;
 			const [key, value] = JSON.parse(line);