341d60d2fe
Replace three uncoordinated logging systems (log.Printf, fmt.Fprintf to stderr, fmt.Println warnings) with structured slog calls. 68 log calls migrated: - log.Printf → slog.Error/Warn/Info (45 calls across 5 files) - fmt.Fprintf(os.Stderr) → slog.Error (23 calls in main.go) Kept unchanged: - fmt.Println/Printf for CLI user output (version, banners, import results) - engine.AddLog for TUI-visible ring buffer (monitoring events) Store migration diagnostics demoted to slog.Debug (silent at default info level). HTTP request logging now structured with method/path/ status/duration/ip attributes.