refactor(logging): Add optional logging support throughout codebase

Add centralized logging utility and optional logger parameters to all
core functions for better observability and debugging capabilities.

New modules:
- utils/logging.py: Centralized logger configuration with console
  and optional file handlers

Enhanced features:
- Added optional logger parameter to all extractor_core functions
- Added logger support to extractor, excel_converter, and auth modules
- Functions remain silent when logger=None (backward compatible)
- Improved environment variable validation in test files

Documentation:
- Added discrete_material_plan_extractor_core.md with complete API
  reference and usage patterns

Benefits:
- Consistent logging format across all components
- Optional debug output for troubleshooting
- No breaking changes - fully backward compatible
- Better error messages and validation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_login.py

@@ -18,7 +18,10 @@ from dotenv import load_dotenv
 load_dotenv(PROJECT_ROOT / ".env")
 
 # Configure browser path
-os.environ["PLAYWRIGHT_BROWSERS_PATH"] = os.getenv("PLAYWRIGHT_BROWSERS_PATH")
+browser_path = os.getenv("PLAYWRIGHT_BROWSERS_PATH")
+if not browser_path:
+    raise ValueError("PLAYWRIGHT_BROWSERS_PATH environment variable is required")
+os.environ["PLAYWRIGHT_BROWSERS_PATH"] = browser_path
 
 print("=" * 60)
 print("Testing Yonyou BIP Login and Logout")
@@ -38,15 +41,24 @@ if not base_url:
 url = f"{base_url.rstrip('/')}/yonbip/resources/uap/rbac/login/main/index.html"
 
 try:
+    # Get required environment variables
+    username = os.getenv('ERP_USERNAME')
+    password = os.getenv('ERP_PASSWORD')
+    headless = os.getenv('ERP_HEADLESS', 'false').lower() in ('true', '1', 'yes')
+    ignore_https_errors = os.getenv('ERP_IGNORE_HTTPS_ERRORS', 'true').lower() in ('true', '1', 'yes')
+    
+    if not username or not password:
+        raise ValueError("ERP_USERNAME and ERP_PASSWORD environment variables are required")
+    
     with sync_playwright() as p:
         print("\n[1/5] Starting browser...")
         browser, context, page, main_frame = login(
             playwright=p,
-            username=os.getenv('ERP_USERNAME'),
-            password=os.getenv('ERP_PASSWORD'),
+            username=username,
+            password=password,
             url=url,
-            headless=os.getenv('ERP_HEADLESS', 'false').lower() in ('true', '1', 'yes'),
-            ignore_https_errors=os.getenv('ERP_IGNORE_HTTPS_ERRORS', 'true').lower() in ('true', '1', 'yes'),
+            headless=headless,
+            ignore_https_errors=ignore_https_errors,
             verbose=True
         )