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/costTracking.test.ts

@@ -1,4 +1,3 @@
-/* eslint-disable max-lines-per-function -- Test suites naturally have many cases */
 import { describe, it, expect } from "vitest";
 import {
   formatCost,