fix(mime): register SVG MIME type in init function

[Xe]

Summary

• Add image/svg+xml MIME type registration for .svg files to ensure SVG images are served with the correct content type
• Uses init() function in internal package for automatic registration when the package is imported

Changes

• Added MIME type registration in internal/slog.go init function
• This ensures SVG files are properly served as image/svg+xml instead of being misidentified

Test plan

• Verify the code compiles successfully
• Test that SVG MIME type is registered correctly
• Ensure no existing functionality is broken

Fixes #SITE-6

[linear]

SITE-6 svg diagrams are broken