feat(components): render semantic diff code blocks

[lodystage]

Summary

• render diff fenced code blocks with semantic addition, deletion, hunk, and metadata rows
• preserve Streamdown code-block controls and support incomplete streaming fences
• add Storybook coverage for headerless snippets and unified patches

Testing

• NODE_ENV=test pnpm --filter @lody/components exec vitest run tests/markdown-streaming-reparse.test.ts (32 tests passed)
• pnpm --filter @lody/components typecheck
• pnpm exec prettier --check packages/components/src/components/ai-gui/markdown-diff-block.tsx packages/components/src/components/ai-gui/markdown-renderer.tsx packages/components/src/stories/MarkdownRenderer.stories.tsx packages/components/src/tailwind/index.css packages/components/tests/markdown-streaming-reparse.test.ts

The targeted Vitest run emits the existing unresolved @tsconfig/node22 warning from packages/acp-extension-claude, then completes successfully.