Improve Mermaid flowchart layout and sizing

[PrzemyslawKlys]

Summary

• Infers deterministic Mermaid flowchart layers from edge direction, including backward-only arrows, so topology reads in the direction the diagram expresses.
• Fits default viewports and node widths to useful content, preserves complete labels through SVG and PNG rendering, and removes health badges when Mermaid carries no health semantics.
• Keeps explicitly requested SVG, PNG, and HTML artifact dimensions unchanged by carrying a typed natural-size policy through generic artifact exports.
• Preserves content-fitted Mermaid tile dimensions, literal apostrophes, and per-node label limits consistently across SVG and PNG rendering.
• Normalizes quoted Mermaid labels and keeps explicit markup dimensions compatible.
• Uses Directory.Build.props as the single package-version source instead of six repeated project versions.

Behavior note

Flowcharts without an explicit viewport now use content fitting by default. Callers that need the former fixed canvas can set FitContent to false. Explicit width or height continues to take precedence for direct and generic artifact output while label-aware node sizing remains enabled.

No package version is bumped and this PR does not publish or release ChartForgeX.

Validation

• Repository quality loop passed on the current implementation: 743 tests, multi-target build, Mermaid.js fixtures, NativeAOT smoke, generated examples, and package creation.
• The final review-driven artifact fix was revalidated with all 743 tests after adding differing-size, missing-size, and caller-model non-mutation coverage.
• Independent read-only review found one P2 and one P3 in the artifact follow-up; both are fixed and the targeted confirmation accepted the implementation.
• All five addressed inline review threads are resolved.

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