Implement user authentication with hashed passwords

Replaces hardcoded admin credentials with a users table in the database, storing hashed passwords and user roles. Updates the login logic in app.py to authenticate against the database using Werkzeug's password hashing utilities. Adds admin credential configuration to config.py and ensures a default admin user is created during database initialization.

utils/database.py

@@ -12,6 +12,8 @@ from contextlib import contextmanager
 from datetime import datetime
 from pathlib import Path
 from typing import Any
+from werkzeug.security import generate_password_hash
+from config import ADMIN_USERNAME, ADMIN_PASSWORD
 
 logger = logging.getLogger('intercept.database')
 
@@ -100,6 +102,31 @@ def init_db() -> None:
             )
         ''')
 
+        # Users table for authentication
+        conn.execute('''
+            CREATE TABLE IF NOT EXISTS users (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                username TEXT UNIQUE NOT NULL,
+                password_hash TEXT NOT NULL,
+                role TEXT NOT NULL,
+                created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+            )
+        ''')
+
+        cursor = conn.execute('SELECT COUNT(*) FROM users')
+        if cursor.fetchone()[0] == 0:
+            from config import ADMIN_USERNAME, ADMIN_PASSWORD
+            
+            logger.info(f"Creating default admin user: {ADMIN_USERNAME}")
+            
+            # Password hashing
+            hashed_pw = generate_password_hash(ADMIN_PASSWORD)
+            
+            conn.execute('''
+                INSERT INTO users (username, password_hash, role)
+                VALUES (?, ?, ?)
+            ''', (ADMIN_USERNAME, hashed_pw, 'admin'))
+
         logger.info("Database initialized successfully")