Refactor: Migrate remaining proxifyImageUrl usages to proxifyImageSrc

Background

During security fix work, we identified that proxifyImageUrl (in packages/ui/lib/old-profixy.ts) is an older proxy function that simply prepends the proxy domain to URLs, while proxifyImageSrc (in packages/ui/lib/proxify-images.ts) uses Base58 encoding which is more secure and consistent with the imagehoster's /p/ endpoint format.

Current State

proxifyImageUrl is still used in several places:

• apps/blog/features/post-editor/select-image-item.tsx
• apps/blog/features/list-of-posts/post-img.tsx
• apps/blog/features/suggestions-posts/card.tsx
• apps/blog/features/post-rendering/lib/renderer.ts

Proposed Changes

1. Migrate all usages of proxifyImageUrl to proxifyImageSrc
2. Once migration is complete, deprecate and remove old-profixy.ts
3. Ensure all images go through the /p/{base58_hash} proxy format

Benefits

• Unified image proxification approach
• More secure URL handling (Base58 encoding neutralizes special characters)
• Cleaner codebase with single proxy function

Notes

This is a refactoring task with low security priority since the remaining usages are in <img src> contexts (not CSS), but unifying the approach improves maintainability.