fix(a11y): trap focus and announce progress in QR and batch modals

[fwseyi]

Adds focus trapping, focus restoration, keyboard shortcuts, and live-region announcements to the QR scanner, QR code modal, and batch withdraw modal. Adds Playwright a11y coverage for all three via Storybook, plus a new pnpm test:a11y script.

Changes

• src/hooks/useFocusTrap.ts — shared hook: traps Tab/Shift+Tab within a dialog, focuses first element on open, restores focus to the trigger on close
• StellarBatchWithdrawModal.tsx — role="dialog", aria-modal, aria-labelledby, Escape-to-close, focus trap, aria-live="polite" on per-item status badges
• QRCodeModal.tsx — focus trap added (existing Escape/initial-focus preserved), aria-label added to the QR SVG (was a serious axe violation — svg-img-alt)
• StellarSend.tsx — focus trap on the scanner dialog, Space toggles camera, U triggers upload-fallback, aria-label on the camera preview
• StellarSplit.tsx — aria-live="polite" aria-atomic="true" on per-row batch-send status (rendered inline, not a modal — confirmed intentional)
• package.json — pnpm test:a11y script added

Tests

tests/a11y/modals.spec.ts — 10 new tests via Storybook (QRCodeModal.stories.tsx, StellarBatchWithdrawModal.stories.tsx, new QRScannerDialog.stories.tsx), covering axe violations, keyboard-only focus trap, and close/Escape behavior for all three dialogs. All 10 passing.

Known pre-existing failure (unrelated to this PR)

tests/a11y/send.spec.ts's two Stellar chain-switch tests fail on both this branch and develop — the Chain sits in a hidden sm:flex container Playwright can't interact with at the default test viewport. Verified via git stash that this predates this PR; out of scope to fix here. Note The batch-send progress dialog (StellarSplit) got lighter test coverage than the other two — one aria-live presence check rather than a full axe scan + keyboard test, since it renders inline rather than as a true modal overlay. Flagging in case a follow-up is wanted for parity. Validation pnpm test:unit → 135/135 passing pnpm format:check → clean pnpm test:a11y → 10/10 new tests passing Closes #160

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[truthixify]

Merged. Focus restoration on close plus live progress announcements, and you added the test:a11y script the acceptance list needed. Thanks @fwseyi.