Refactor admin panel and add migration documentation

- Add comprehensive migration guides (DEPLOYMENT_MIGRATION.md, DIRECTORY_STRUCTURE.md, MIGRATION_CHECKLIST.md)
- Refactor admin panel: split add.php, create reusable header/footer
- Update styles: admin.css, common.css, main.css
- Improve public pages: index.php, memoire.php
- Reorganize database documentation into database/docs/
- Update .gitignore and justfile

This prepares for migration to public/ directory structure

lib/cache/rate_limit/ad921d60486366258809553a3db49a4a.json

@@ -1 +1 @@
-[1770317579]
+[1770319036]

lib/cache/rate_limit/f528764d624db129b32c21fbca0cb8d6.json

@@ -1 +1 @@
-[1770318922,1770318923,1770318924,1770318926,1770318930]
+[1770322829]