feat(config): add LOG_LEVEL setting and configure root logging at startup

- Add `log_level` setting to config.py (default: INFO, env: LOG_LEVEL)
- Configure Python root logger in main.py with standard precedence:
  LOG_LEVEL explicit > DEBUG=true implies DEBUG > default INFO
- Add timestamp to log format for production readability
- Suppress noisy third-party loggers at DEBUG level
- Add comprehensive debug logging to all auth functions
- Add LOG_LEVEL/DEBUG to .env.demo and ConfigurationGuide.md
- Add tests for logging config and auth debug output

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

.env.demo

@@ -7,6 +7,13 @@ GOTENBERG_URL=http://gotenberg:3000
 ALLOW_FILE_DELETE=true  # Allow deletion of file records
 COMPLIANCE_ENABLED=true  # Enable compliance templates dashboard (GDPR, HIPAA, SOC 2)
 
+# **Logging**
+# LOG_LEVEL controls the Python root-logger level.
+# Accepted values: DEBUG, INFO, WARNING, ERROR, CRITICAL (default: INFO).
+# When DEBUG=true and LOG_LEVEL is not set, the level is automatically lowered to DEBUG.
+# LOG_LEVEL=INFO
+# DEBUG=false
+
 # **UI / Appearance**
 # Default colour scheme: system (follow OS), light, or dark
 # Individual users can always override with the navbar dark-mode toggle.