chore(deps): upgrade WebMCP packages to 4.0.0

[MiguelsPizza]

What changed

• Upgraded the chat UI and MCP server apps to the stable @mcp-b/* 4.0.0 packages.
• Kept the Playwright smoke tests aligned with the v4 runtime behavior and local dev origins.
• Regenerated the pnpm lockfile with pnpm 10.

Why

WebMCP 4.0.0 is now published on npm, so the demo apps should validate the same stable package versions users install.

References:

• npm: @mcp-b/react-webmcp
• npm: @mcp-b/transports
• npm: @mcp-b/webmcp-ts-sdk
• npm: @mcp-b/global
• WebMCP release work: feat: align WebMCP runtime with Chrome 152 npm-packages#262

Validation

• pnpm check
• pnpm build
• pnpm test