Fix bugs, convert thumbnail to png, add context menu

backend/app/auth/hashing.py

@@ -0,0 +1,20 @@
+"""Argon2id password hashing and verification."""
+
+from argon2 import PasswordHasher
+from argon2.exceptions import VerifyMismatchError
+
+# Argon2id is the default for PasswordHasher
+ph = PasswordHasher()
+
+def hash_password(password: str) -> str:
+    """Hash a plaintext password."""
+    return ph.hash(password)
+
+def verify_password(hashed: str, password: str) -> bool:
+    """Verify a password against a hash. Returns True if matched."""
+    try:
+        ph.verify(hashed, password)
+        # Note: We skip check_needs_rehash() for simplicity in this single-user app.
+        return True
+    except VerifyMismatchError:
+        return False