fix(a11y): harden shared interactive controls

[beruro]

Summary

• use native buttons for DateRange and macOS window controls instead of clickable divs with local keyboard emulation
• expose SearchInput replace-toggle label and expanded state
• add dialog/modal semantics, labelled close control, and Escape cleanup to image preview
• make virtualized session rows focusable and Enter/Space operable without changing their measured row element
• replace DateRange arbitrary spacing/typography values with project scale utilities

Validation

• focused accessibility/SearchInput Vitest suites: 4 passed
• pnpm exec tsc --noEmit --pretty false
• Prettier and ESLint on all changed TypeScript/TSX files
• git diff --check

Frontend UI audit

7 fixes applied, 4 patterns kept with documented reasons, 0 remaining abstraction candidates. The report is included at docs/frontend-ui-audit-2026-07-24/SharedComponentAccessibility.md.

Architecture audit

Covered compilation and shared interaction-state semantics. The virtualized row keeps its measured DOM ownership; no persistence, wire, initialization, resolver, or background lifecycle behavior changes.

[beruro]

Restacked onto #512. This PR now contains only the semantic-button accessibility delta and focused contract coverage (4 files). Merge #512 first, then retarget to develop for CI.