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)

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"fmt"
 	"log/slog"
 	"os"
 	"os/signal"
@@ -10,6 +11,7 @@ import (
 	"dbbackup/cmd"
 	"dbbackup/internal/config"
 	"dbbackup/internal/logger"
+	"dbbackup/internal/metrics"
 )
 
 // Build information (set by ldflags)
@@ -42,6 +44,20 @@ func main() {
 	// Initialize logger
 	log := logger.New(cfg.LogLevel, cfg.LogFormat)
 
+	// Initialize global metrics
+	metrics.InitGlobalMetrics(log)
+	
+	// Show session summary on exit
+	defer func() {
+		if metrics.GlobalMetrics != nil {
+			avgs := metrics.GlobalMetrics.GetAverages()
+			if ops, ok := avgs["total_operations"].(int); ok && ops > 0 {
+				fmt.Printf("\n📊 Session Summary: %d operations, %.1f%% success rate\n", 
+					ops, avgs["success_rate"])
+			}
+		}
+	}()
+
 	// Execute command
 	if err := cmd.Execute(ctx, cfg, log); err != nil {
 		log.Error("Application failed", "error", err)