fix: trim leading/trailing whitespace on input to prevent load failure

[rdwz]

Summary

• Pasted SVG markup can include a stray leading newline (or other whitespace) before the <?xml ...?> declaration.
• OXVG's parser rejects that as a misplaced XML declaration, surfacing a "Load failed" error to the user even though the SVG itself is valid.
• Trim the input string before handing it to oxvg.wrapOriginal so this case loads successfully.

Test plan

• Paste SVG markup with a leading blank line/whitespace before <?xml ...?> and confirm it loads instead of showing "Load failed".
• Paste/load normal SVG markup (no leading whitespace) and confirm behavior is unchanged.

🤖 Generated with Claude Code