Enhance DatabaseManager with logging, validation, and cleanup

- Added detailed logging for database initialization and connection handling.
- Implemented configuration validation and sanity checks during initialization.
- Introduced `close()` method to properly release database resources.
- Updated `MediaManagerApplication` to invoke `DatabaseManager.close()` on shutdown.
- Updated `.gitignore` to exclude sensitive configuration files while allowing example files.

.gitignore

@@ -44,3 +44,11 @@ config-local.properties
 pipes/
 *.log
 /.idea/
+
+ Configuration files with sensitive credentials
+# These files contain database passwords and API keys and should never be committed
+src/main/resources/config.properties
+src/main/resources/application.properties
+
+# Allow example configuration files to be committed
+!src/main/resources/*.properties.example