Fix PowerPoint relationship copying edge cases

[sergey-tihon]

Summary

• Copy a1611:picAttrSrcUrl online-image relationship IDs when publishing slides.
• Drop zero-byte custom XML parts referenced by p:custData and prune dangling p:custDataLst markup to avoid PowerPoint repair prompts.
• Normalize non-standard SVG image MIME type image/svg to image/svg+xml during image copy.
• Bump CLI changelog to 0.1.2 for the next package publish.

Fixed Issues

• Online image source URL relationships were not rewritten, leaving copied slides with stale r:id references.
• Empty custom XML parts could be copied into generated decks and trigger PowerPoint repair dialogs.
• Mixed/non-standard SVG content types could produce package inconsistencies that PowerPoint repairs.

Validation

• dotnet csharpier format Clippit/PowerPoint/Fluent/FluentPresentationBuilder.Copy.cs Clippit.Tests/PowerPoint/PresentationBuilderSlidePublishingTests.Fluent.cs
• dotnet test --project Clippit.Tests/ --treenode-filter "///PresentationBuilderSlidePublishingTests/CustData"
• dotnet run --project Clippit.Cli/Clippit.Cli.csproj -- version --format json

[Copilot]

Pull request overview

This PR hardens the slide publishing/copy pipeline against several PowerPoint package/relationship edge cases that can lead to stale references or repair prompts when opening generated decks.

Changes:

• Rewrites a1611:picAttrSrcUrl online-image relationship IDs during content part copying.
• Skips copying zero-byte CustomXmlParts referenced by p:custData and prunes dangling p:custDataLst markup.
• Normalizes non-standard SVG MIME type image/svg to image/svg+xml during image part copy, and bumps CLI changelog to 0.1.2.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
Clippit/PtOpenXmlUtil.cs	Adds A1611.picAttrSrcUrl XName constant used for relationship rewrite detection.
Clippit/PowerPoint/Fluent/FluentPresentationBuilder.Copy.cs	Implements the relationship rewrite + empty customXml pruning + SVG content-type normalization.
Clippit.Tests/PowerPoint/PresentationBuilderSlidePublishingTests.Fluent.cs	Adds a regression test for skipping empty CustomXmlPart referenced by p:custData.
Clippit.Cli/CHANGELOG.md	Adds 0.1.2 changelog entry for the upcoming CLI publish.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.