Fix generated source image links

[sunilkumarvalmiki]

Summary

• Generate source-summary image links as ../media/... so they resolve from wiki/sources/*.md in external Markdown editors.
• Normalize the new source-relative shape back to wiki/media/... for in-app preview loading.
• Keep raw-source jump helpers compatible with both existing and new image link shapes.

Evidence

Before: #170 reports that generated source Markdown used media/... links, which do not resolve from files under wiki/sources/ when opened outside the app.
After: embedded-image sections in source summaries point to ../media/..., while the app still resolves both media/... and ../media/... to the same media files.

Tests

• npm run test:mocks -- src/lib/extract-source-images.test.ts src/lib/markdown-image-resolver.test.ts src/lib/raw-source-resolver.test.ts
• npm run test:mocks
• npm run typecheck
• npm run build
• git diff --check

Closes #170

[nashsu]

please fix the conflicts, thx