Typo: `retun` should be `return`

## 🤖 AI Discovered Bug

**Description:** Python keyword `retun` is misspelled. It should be `return`. This causes a `NameError` at runtime because Python treats it as an identifier, not a keyword.

**File:** `app.py`, **Line 40:** `retun check_password_hash(self.password_hash, password)`

**File:** app.py

This issue was automatically generated by AutoPR AI Scanner.