Implement database connection pooling with context manager pattern

- Added DBUtils PooledDB for intelligent connection pooling
- Created db_pool.py with lazy-initialized connection pool (max 20 connections)
- Added db_connection_context() context manager for safe connection handling
- Refactored all 19 database operations to use context manager pattern
- Ensures proper connection cleanup and exception handling
- Prevents connection exhaustion on POST requests
- Added logging configuration for debugging

Changes:
- py_app/app/db_pool.py: New connection pool manager
- py_app/app/logging_config.py: Centralized logging
- py_app/app/__init__.py: Updated to use connection pool
- py_app/app/routes.py: Refactored all DB operations to use context manager
- py_app/app/settings.py: Updated settings handlers
- py_app/requirements.txt: Added DBUtils dependency

This solves the connection timeout issues experienced with the fgscan page.

py_app/app/__init__.py

@@ -1,10 +1,17 @@
 from flask import Flask
 from datetime import datetime
+import os
 
 def create_app():
     app = Flask(__name__)
     app.config['SECRET_KEY'] = 'your_secret_key'
     
+    # Initialize logging first
+    from app.logging_config import setup_logging
+    log_dir = os.path.join(app.instance_path, '..', 'logs')
+    logger = setup_logging(app=app, log_dir=log_dir)
+    logger.info("Flask app initialization started")
+    
     # Configure session persistence
     from datetime import timedelta
     app.config['PERMANENT_SESSION_LIFETIME'] = timedelta(days=7)
@@ -15,14 +22,21 @@ def create_app():
     # Set max upload size to 10GB for large database backups
     app.config['MAX_CONTENT_LENGTH'] = 10 * 1024 * 1024 * 1024  # 10GB
     
+    # Note: Database connection pool is lazily initialized on first use
+    # This is to avoid trying to read configuration before it's created
+    # during application startup. See app.db_pool.get_db_pool() for details.
+    logger.info("Database connection pool will be lazily initialized on first use")
+    
     # Application uses direct MariaDB connections via external_server.conf
-    # No SQLAlchemy ORM needed - all database operations use raw SQL
+    # Connection pooling via DBUtils prevents connection exhaustion
 
+    logger.info("Registering Flask blueprints...")
     from app.routes import bp as main_bp, warehouse_bp
     from app.daily_mirror import daily_mirror_bp
     app.register_blueprint(main_bp, url_prefix='/')
     app.register_blueprint(warehouse_bp, url_prefix='/warehouse')
     app.register_blueprint(daily_mirror_bp)
+    logger.info("Blueprints registered successfully")
 
     # Add 'now' function to Jinja2 globals
     app.jinja_env.globals['now'] = datetime.now