Update PWA and favicon icons

[code-by-sia]

Summary

• Adds a new SVG-first OpenWebSheet app icon and regenerates the favicon/PWA PNG assets from it.
• Updates the manifest with SVG, 64, 128, 192, 256, and 512 icon entries plus maskable PNG purposes.
• Links SVG/PNG favicons, Apple touch icon, manifest, and theme color from the app shell; rebuilds docs assets for GitHub Pages.

Validation

• npm test
• npm run typecheck
• npm run build
• Parsed public and docs manifests as JSON after build.

Note: npm run build still reports the existing direct eval warning in src/lib/core/formula/Evaluator.ts; it does not block the build.