Added exporting to svg

[breadddevv]

Changes

• Added downloadSVG function to utils/export.js. Which basically wraps the canvas pixel output in an <svg> <image> element and triggers a .svg download
• Replaced the single Download button with a split button: left side downloads PNG directly, chevron opens a dropdown to choose PNG or SVG
• Dropdown closes on outside click via a useEffect listener
• Fixed split button margin issue — moved spacing to the .App-download-split wrapper and zeroed it on child buttons so the two halves sit flush
• Fixed malformed --loading-text: #rgb(...) value in dark mode CSS

[vercel]

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