feat: add common utilities and feedback handling scripts

- Introduced common.js for shared functions including API calls, error reporting, and UI helpers.
- Implemented feedback.js for the feedback reporting page, including form handling and displaying feedback status.
- Added layout.js for managing galaxy and section layouts in the visualization.
- Created login.js for user authentication with session management.
- Developed search.js for term searching based on user input and synonyms.
- Implemented signup.js for user registration with validation and immediate login.

.gitignore

@@ -0,0 +1,12 @@
+.venv/
+__pycache__/
+*.pyc
+.pytest_cache/
+# 실행 중 생기는 DB·비밀값 (atlas.json 은 파이프라인 결과라 커밋)
+data/atlas.db
+data/atlas.db-*
+data/.secret
+data/.admin_password
+data/drafts/in_*.json
+.DS_Store
+backups/