docs: add comprehensive multi-language documentation (en-US + pt-BR)

[devin-ai-integration]

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
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Summary

Complete multi-language documentation overhaul for QRCoder.Core.

README files

• Rewrote README.md in English (en-US) as the default language with comprehensive sections: output formats table, payload types table, quick start, error correction levels, repo structure, CI/CD, and contributing guide
• Created README.pt-br.md with full Portuguese (pt-BR) translation

NuGet package README

• Rewrote QRCoder.Core/Assets/nuget-readme.md in English with:
  • Quick start example
  • Output formats table with inline code examples
  • Multiple formats example
  • Payload types examples (WiFi, URL, Email, Phone, vCard)
  • Error correction levels reference
  • Links to repository, usage guide, and issues

XML documentation improvements

Improved class-level /// <summary> on all public types:

• Abstractions: AbstractQRCode — lifecycle management and QRCodeData access
• Models: QRCodeData — module matrix storage, QRR serialization; Size — rendering dimensions
• Renderers: QRCode, PngByteQRCode, SvgQRCode, ArtQRCode, AsciiQRCode, Base64QRCode, PdfByteQRCode, PostscriptQRCode, SKBitmapByteQRCode
• Exceptions: DataTooLongException — payload capacity exceeded
• Extensions: SKColorExtensions — hex conversion; StringValueAttribute, CustomExtensions

Build

• dotnet build QRCoder.Core.sln --configuration Release passes successfully across all 4 targets (netstandard2.1, net8.0, net10.0, net48)

Link to Devin session: https://app.devin.ai/sessions/e7852e5f759e4ba9a2ed414a0f8cc7e6
Requested by: @afonsoft

[devin-ai-integration]

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud