Prepare ChartForgeX 1.6.0 typed interchange release

[PrzemyslawKlys]

Summary

• advances the shared ChartForgeX package line to 1.6.0 for the typed, versioned semantic visual-artifact interchange API already merged on main
• refreshes release notes across the core, interactivity, markup, and Mermaid packages
• updates the executable NuGet metadata contract to require the synchronized 1.6.0 release lane

Why a new version is required

The immutable public ChartForgeX 1.5.0 package was built from pre-redesign commit 62fdc741, while its tag now points at the later typed-interchange merge 889a210d. The public payload therefore lacks VisualArtifactInterchangeEnvelope and related typed APIs. A new public version is required; republishing 1.5.0 is not possible.

This PR prepares source/package metadata only. It does not publish packages.

Validation

• full Build.ps1 -Configuration Release quality loop passed
• 778/778 tests passed
• all 31 Mermaid fixtures passed
• NativeAOT, examples, and package generation passed
• generated 1.6.0 packages contain net472, netstandard2.0, net8.0, and net10.0 assets; the core XML surface contains the typed interchange envelope and semantic models

[chatgpt-codex-connector]

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