implement user authentication flow, session management, and admin user management capabilities

main.py

@@ -80,17 +80,22 @@ def init_db():
         )
     ''')
     
-    # Create default admin if no users exist
+    # Create or update default admin if no users exist or only one user exists
     c.execute('SELECT COUNT(*) FROM users')
-    if c.fetchone()[0] == 0:
+    count = c.fetchone()[0]
+    if count == 0:
         print("Creating default admin user...")
         admin_hash = get_password_hash(WEB_PASSWORD)
         c.execute('INSERT INTO users (username, hashed_password, is_admin) VALUES (?, ?, ?)',
                   ('admin', admin_hash, 1))
-        
-        # Associate existing instances with the new admin user
-        admin_id = c.lastrowid
-        c.execute('UPDATE instances SET user_id = ? WHERE user_id IS NULL', (admin_id,))
+    elif count == 1:
+        # If there's only one user and it's 'admin', ensure its password matches WEB_PASSWORD
+        c.execute('SELECT id, username FROM users LIMIT 1')
+        user = c.fetchone()
+        if user[1] == 'admin':
+            print("Ensuring admin password matches WEB_PASSWORD...")
+            admin_hash = get_password_hash(WEB_PASSWORD)
+            c.execute('UPDATE users SET hashed_password = ? WHERE id = ?', (admin_hash, user[0]))
         
     conn.commit()
     conn.close()