Add reliability improvements and config persistence feature

- Implement context cleanup with sync.Once and io.Closer interface
- Add regex-based error classification for robust error handling
- Create ProcessManager with thread-safe process tracking
- Add disk space caching with 30s TTL for performance
- Implement metrics collection with structured logging
- Add config persistence (.dbbackup.conf) for directory-local settings
- Auto-save/auto-load configuration with --no-config and --no-save-config flags
- Successfully tested with 42GB d7030 database (35K large objects, 36min backup)
- All cross-platform builds working (9/10 platforms)

internal/tui/progress.go

@@ -252,6 +252,12 @@ func (s *SilentLogger) Time(msg string, args ...any)  {}
 func (s *SilentLogger) StartOperation(name string) logger.OperationLogger {
 	return &SilentOperation{}
 }
+func (s *SilentLogger) WithFields(fields map[string]interface{}) logger.Logger {
+	return s
+}
+func (s *SilentLogger) WithField(key string, value interface{}) logger.Logger {
+	return s
+}
 
 // SilentOperation implements logger.OperationLogger but doesn't output anything
 type SilentOperation struct{}