Feature/fe add unit tests for transaction filter sidebar

[Thosine-01]

Closes #790

What this PR does

Adds a comprehensive unit test suite for the TransactionFilterSidebar component as part of the UX enhancement initiative. Also includes two small accessibility fixes to the component that were required to make the tests correct and meaningful.

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Changes made

frontend/src/components/TransactionFilterSidebar.test.tsx

• Replaced the existing stub test file with a full 68-test suite
• Tests are organised into 6 clearly labelled suites
• Uses @testing-library/react with vitest and jsdom
• framer-motion is mocked to forward all HTML/ARIA attributes correctly so accessibility assertions are reliable

frontend/src/components/TransactionFilterSidebar.tsx

Two accessibility patches were required:

1. Added aria-label="Clear search" to the clear-search button — it previously had no accessible label, making it untestable and inaccessible to screen readers
2. Added aria-hidden="true" to the SyncSpinner wrapper span inside asset buttons — without this, the spinner text was concatenated into the button's accessible name (e.g. "XLMSyncing…" instead of "XLM"), which is both a test failure and an a11y bug

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Test coverage breakdown

Suite	What is tested	Tests
1 · Rendering	Desktop panel, mobile drawer, all fields, status options, asset buttons, controlled values	16
2 · Interactions	Search input, clear search, status select (all 4 options), asset buttons (all 3), date inputs, Clear All button	17
3 · Pending visual feedback	searchSyncPending state, isFilterPending state, combined anyPending state, aria-busy, dashed borders, opacity, hint text, aria-live	20
4 · Accessibility	Input types, placeholders, aria-hidden on decorative SVGs, label linkage, group roles	7
5 · Mobile drawer	Open/close via button, backdrop click, filter interactions inside drawer	5
6 · Edge cases	Missing onClose prop, all flags active simultaneously, disabled+pending Clear All	3
Total		68

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Test results

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