[llbbl]

Summary

• add viewport-fit safe-area support to Vue and Svelte chat pages
• make modern chat controls, message content, and composer layouts mobile-safe at 320px
• add shared Playwright coverage for viewport metadata, overflow, touch targets, long content, and sticky composer behavior
• document the mobile behavior and release verification path

Validation

• PASS code review: no blocking findings in mobile layout, safe-area handling, touch targets, overflow, accessibility semantics, or test coverage
• composer test: PASS (179 tests, 553 assertions)
• composer test:integration: PASS (15 tests, 85 assertions)
• composer test:integration:websocket: PASS (4 tests, 21 assertions)
• corepack pnpm@10.34.5 check: PASS
• corepack pnpm@10.34.5 build: PASS
• corepack pnpm@10.34.5 e2e: PASS (6 tests)
• PHPStan: PASS
• PHP CS Fixer sequential dry-run: PASS
• Composer audit: clean
• pnpm production audit: clean
• git diff --check: PASS
• Lighthouse 13.4.1 authenticated mobile: Vue accessibility 100 / best practices 96; Svelte accessibility 100 / best practices 96
• independent JS/TypeScript review: PASS
• independent Svelte review: PASS
• mutation testing: intentionally not run; manual-only per project workflow

Closes #125