feat: 검색 페이지에 대한 디자인 시스템 적용

[MTtankkeo]

변경 사항

• 검색 페이지 전반에 GDS 디자인 시스템을 적용
• 검색 결과 화면의 공통 UI 관련 로직 정리
• 검색 전/결과 없음 상태를 SearchWelcomeState, SearchEmptyState로 분리
• 피드/유저/게시글 검색 결과 리스트의 여백, 반응형 레이아웃, 빈 상태 처리 정리
• 게시글 목록 UI를 GrimityPostView로 공통화하여 게시판/검색 페이지에서 재사용
• 게시글 검색 결과에 북마크 표시 및 저장/해제 동작 추가

피그마 참고

• 모바일: https://www.figma.com/design/BA5LeHKF3saevi3poE85n2/Grimity_APP?node-id=1034-87290&m=dev
• 테블릿: https://www.figma.com/design/BA5LeHKF3saevi3poE85n2/Grimity_APP?node-id=1001-272076&m=dev

[gemini-code-assist]

Code Review

This pull request refactors several enums to simplify JSON serialization and migrates the board and search views to use GDS (Grimity Design System) components, including the introduction of GrimityPostView and GdsUserCard. It also adds bookmarking capabilities to post cards and refactors search tab views to handle empty and welcome states. The review feedback highlights critical compilation errors in the search tag views due to incorrect scroll direction types, a JSON serialization mismatch in the PostType enum, and a UX regression in BoardView where a missing scroll controller prevents scrolling to the top on page changes. Additionally, minor issues regarding unsupported sort options and incorrect button labels in the search user tab were identified.

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