Support vector SVG image imports

[boomzero]

Summary

• keep newly imported SVGs as vector data URLs by normalizing root width/height instead of rasterizing to PNG
• normalize SVGs for image add, clipboard paste, and slide background uploads
• add SVG helper tests for UTF-8, viewBox/partial dimensions, malformed XML, MIME detection, and data URL variants

Verification

• npm exec vitest -- run tests/renderer/lib/svg.test.ts
• npm run typecheck
• npm run lint
• Manual QA passed with SVG fixtures for viewBox-only, percentage dimensions, explicit dimensions, no dims/no viewBox, non-ASCII text, script smoke, malformed SVG rejection, and background error handling

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 56eb76c1fe

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[boomzero]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 6d301b6e5b

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".