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.

src/main/resources/config.properties.example

@@ -0,0 +1,24 @@
+# Database Configuration
+db.url=jdbc:postgresql://localhost:5432/mediamanager
+db.username=mediamanager
+db.password=changeme
+db.driver=org.postgresql.Driver
+
+# HikariCP Connection Pool Settings
+db.pool.maximum-pool-size=10
+db.pool.minimum-idle=2
+db.pool.connection-timeout=30000
+db.pool.idle-timeout=600000
+db.pool.max-lifetime=1800000
+
+# Hibernate Settings
+hibernate.dialect=org.hibernate.dialect.PostgreSQLDialect
+hibernate.hbm2ddl.auto=update
+hibernate.show_sql=false
+hibernate.format_sql=true
+
+# IPC Configuration
+ipc.pipe.name=mediamanager-pipe
+ipc.pipe.path=/tmp/mediamanager
+ipc.buffer.size=8192
+