feat(ui): add close button to mobile sidebar

[d-oit]

Add a dedicated focusable Close button to the mobile sidebar header for improved keyboard and screen-reader accessibility. Includes full responsive Playwright E2E tests and pristine 0-warning linting setup.

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PR created automatically by Jules for task 2726480197960101131 started by @d-oit

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Project	Deployment	Actions	Updated (UTC)
do-web-doc-resolover	Ready	Preview, Comment	Jul 24, 2026 3:05pm

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Up to standards ✅

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