Fix Week 2 SQLite demo database path and add 'which is my database?' comment

[enaguero]

Summary

• The Week 2 demo API in class-2/week2-sqlite/main.py connected to database.db, but Part 1 of the lab creates university.db. SQLite silently created an empty database.db, so /students failed with no such table: students.
• Point the demo at university.db, matching the lab handout (part-1.md and part-2.md).
• Add a student-facing comment above the path: check where you are connecting and ask "which one is my database?", plus a note that sqlite3.connect() creates an empty file when the path is wrong, so the symptom is "no such table" rather than "file not found".
• Add university.db to .gitignore (same convention as app.db / auth.db), since Part 1 has students generate and reset it from setup_students.sql.

This is also the first commit of the week2-sqlite demo project (main.py, requirements.txt, setup_students.sql).

Test plan

• In class-2/week2-sqlite, create the database if it does not exist yet: sqlite3 -bail university.db ".read setup_students.sql"
• Activate .venv, run uvicorn main:app --reload, open http://127.0.0.1:8000/students
• Expect a JSON list of the three students (Ada Lovelace, Alan Turing, Grace Hopper)

🤖 Generated with Claude Code