feat: add Blazor WebAssembly example

[Happypig375]

Closes #184

Summary

• add a .NET 10 Blazor WebAssembly example using SKCanvasView and MathPainter
• support live valid/invalid and multiline formula updates, responsive logical-DPI sizing, accessible text, and safe component disposal
• add focused editor-state tests and a pinned Playwright browser smoke
• add a least-privilege CI workflow that installs wasm-tools, performs the native WASM publish, and exercises rendering in Chromium

Validation

• CSharpMath.Blazor.Example.Tests: 2 passed
• node --check browser-smoke/smoke.mjs
• browser smoke rejects blank white canvases and verifies initial, dynamic, multiline, resize, error, and navigation behavior
• independent validation and review: approved

Local native publish is unavailable because this machine does not have the wasm-tools workload; the PR's Blazor workflow is the required native publish/browser acceptance gate.