Phase 1 Sprint 2+3: design system and composer a11y

[Pterjudin]

Summary

Completes Phase 1 Sprint 2 (design system) and Sprint 3 (a11y) for the chat composer shell.

Sprint 2 — Design system

• Activate .btn, .btn-primary, .btn-secondary, .btn-submit, .btn-stop, .input, .dropdown, .cortex-composer-shell in styles.css using --cortex-* tokens
• Theme-aware submit button (dark: high-contrast pill; light: brand purple)
• Replace hardcoded #030304 / bg-white in VoidChatArea with design-system classes
• Suggested prompts use .btn-secondary + .cortex-prompt-chip
• Add designSystem.test.ts CSS contract (4 checks) → test-phase0-qa now 92 tests

Sprint 3 — Accessibility

• ContextUsageBar — proper role="progressbar" with aria-valuenow/min/max
• Suggested prompts — div → button
• User message bubble — clickable bubble + edit control are real buttons with labels
• Composer close (X) — button with aria-label
• Tool headers — keyboard support (Enter/Space) + role="button" on collapsible headers

Test plan

• npm run buildreact
• npm run test-phase0-qa — 92 passing
• Manual: dark + light theme — composer input, submit/stop icons readable
• Manual: Tab to suggested prompts / edit message / tool headers; activate with Enter
• Manual: context usage bar announced by screen reader as progressbar

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