revert: revert image optimization commit 1ed087fb

[tasoo-oos]

Description

• release 대상 PR에서는 이미지 압축 워크플로우가 실행되지 않도록 수정했습니다.
• GitHub Actions가 다시 압축한 배너 이미지를 기존 원본 이미지로 복구했습니다.
• 문제가 있던 2026.05.27 릴리즈 revert 상태는 유지했습니다.

Additional context

• git merge-tree --write-tree origin/release HEAD 통과
• git merge-tree --write-tree origin/main HEAD 통과
• CI 통과

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Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines
• Read the Contributing Guidelines and follow the Commit Convention
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.

[github-actions]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 76.2%, saving 1.4 MB.

Filename	Before	After	Improvement	Visual comparison
apps/frontend/public/banners/main_banner.png	1.2 MB	236.4 KB	80.0%	View diff
apps/frontend/public/banners/mainpage_middle_banner.png	729.5 KB	217.7 KB	70.2%	View diff