test: add component logic tests and clean up eslint directives

Adds mirror-function tests for five Svelte components (HighlightedText,
CliVersion, AchievementNotification, StatusBar, ConversationTabs) and
removes stale eslint-disable comments from existing store test files.

src/lib/stores/notifications.test.ts

@@ -1,4 +1,3 @@
-/* eslint-disable @typescript-eslint/init-declarations -- Variables reassigned in beforeEach */
 import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
 import { writable } from "svelte/store";