feat: implement internationalization for UI text, refactor localStorage keys, and add input validation for state setters.

src/api.js

@@ -1,5 +1,15 @@
+/**
+ * API header factories for the Bessa REST API and GitHub API.
+ * All fetch calls in the app route through these helpers to ensure
+ * consistent auth and versioning headers.
+ */
 import { API_BASE, GUEST_TOKEN, CLIENT_VERSION } from './constants.js';
 
+/**
+ * Returns request headers for the Bessa REST API.
+ * @param {string|null} token - Auth token; falls back to GUEST_TOKEN if absent.
+ * @returns {Object} HTTP headers for fetch()
+ */
 export function apiHeaders(token) {
     return {
         'Authorization': `Token ${token || GUEST_TOKEN}`,
@@ -9,6 +19,11 @@ export function apiHeaders(token) {
     };
 }
 
+/**
+ * Returns request headers for the GitHub REST API v3.
+ * Used for version checks and release listing.
+ * @returns {Object} HTTP headers for fetch()
+ */
 export function githubHeaders() {
     return { 'Accept': 'application/vnd.github.v3+json' };
 }