feat: update portfolio content - projects, skills, experience, education

- Replace projects with current work (Hongik, SION, A301, tolelog, No-Ill)
- Add project period display
- Add SSAFY embedded track to Education and Experience
- Add No-Ill PM role to Experience
- Update Skills: remove unused (Django, Express.js, Unreal), add actual stack (Redis, WebSocket, JWT, PostgreSQL, LevelDB, CI/CD, Git, Jira)
- Update About section to reflect current status

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

js/main.js

@@ -22,6 +22,7 @@ function renderProjects() {
           '<span class="project-card-name">' + p.name + "</span>" +
           '<span class="project-card-category">' + p.category + "</span>" +
         "</div>" +
+        (p.period ? '<span class="project-card-period">' + p.period + '</span>' : '') +
         '<p class="project-card-desc">' + p.description + "</p>" +
         '<div class="project-card-tags">' + tags + "</div>" +
         links +