Add roadmap management feature with database schema and user management

- Implemented roadmap.php for displaying and managing roadmap items with filters for quarter and status.
- Created schema.sql to define the database structure for users, invites, daily plans, tasks, brainstorm sessions, brainstorm cards, roadmap items, and integrations.
- Developed users.php for admin panel to manage team members and invitations, including functionality to create and revoke invites.

.gitignore

@@ -0,0 +1,10 @@
+# Environment
+.env
+.env*.local
+
+# Systeem & Editor
+.DS_Store
+Thumbs.db
+*.log
+.vscode/
+.idea/