[DASHBOARD] Set up Flask app skeleton and folder structure

[ezehf2]

Create the initial Flask application structure ready for Sprint 3 development. This means creating app.py with a basic Flask app that runs locally, a templates/ folder with a base HTML file, and a static/ folder for CSS and JavaScript. The app does not need to display real data yet — a placeholder homepage confirming the app runs is enough. This gives the dashboard a committed starting point in the repo before active development begins in Sprint 3.