fix: backup validation display and debug logging

- Add 4-branch template guard to handle zero-value DumpValidation
  (shows "–" instead of misleading "Hiba" when validation never ran)
- Add debug logging to ValidateDump for all code paths
- Add cross-check re-validation in RefreshCache to heal stale
  lastDBDump validation state from disk

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/internal/backup/backup.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"log"
+	"path/filepath"
 	"strings"
 	"sync"
 	"time"
@@ -420,7 +421,8 @@ func (m *Manager) RefreshCache(nextDBDump, nextBackup time.Time) {
 	if stats, err := m.restic.Stats(); err == nil {
 		status.RepoStats = stats
 	}
-	if files, err := ListDumpFiles(m.cfg.Paths.DBDumpDir); err == nil {
+	files, filesErr := ListDumpFiles(m.cfg.Paths.DBDumpDir)
+	if filesErr == nil {
 		status.DumpFiles = files
 	}
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
@@ -429,6 +431,25 @@ func (m *Manager) RefreshCache(nextDBDump, nextBackup time.Time) {
 		status.DiscoveredDBs = dbs
 	}
 
+	// Cross-check: if LastDBDump results have empty validation but files exist,
+	// re-validate from disk. This handles controller restarts and race conditions.
+	if m.lastDBDump != nil && filesErr == nil {
+		fileValidation := make(map[string]DumpValidation) // keyed by filename
+		for _, f := range files {
+			fileValidation[f.FileName] = f.Validation
+		}
+		for i, r := range m.lastDBDump.Results {
+			if !r.Validation.Valid && r.Validation.Error == "" && r.FilePath != "" {
+				filename := filepath.Base(r.FilePath)
+				if fv, ok := fileValidation[filename]; ok {
+					m.lastDBDump.Results[i].Validation = fv
+					m.logger.Printf("[INFO] Re-validated %s from disk: valid=%v tables=%d",
+						filename, fv.Valid, fv.TableCount)
+				}
+			}
+		}
+	}
+
 	// Fill in dynamic fields under lock
 	m.mu.Lock()
 	status.Running = m.running

controller/internal/backup/dbdump.go

@@ -231,6 +231,7 @@ func DumpOne(ctx context.Context, db DiscoveredDB, dumpDir string, logger *log.L
 
 // ValidateDump checks a SQL dump file for basic structural integrity.
 func ValidateDump(filePath string, dbType DBType) DumpValidation {
+	log.Printf("[DEBUG] ValidateDump: %s (type=%s)", filePath, dbType)
 	stat, err := os.Stat(filePath)
 	if err != nil {
 		return DumpValidation{Error: fmt.Sprintf("stat failed: %v", err)}
@@ -243,12 +244,14 @@ func ValidateDump(filePath string, dbType DBType) DumpValidation {
 
 	if stat.Size() < 100 {
 		v.Error = "dump file too small (< 100 bytes)"
+		log.Printf("[WARN] ValidateDump FAIL: %s — %s", filePath, v.Error)
 		return v
 	}
 
 	data, err := os.ReadFile(filePath)
 	if err != nil {
 		v.Error = fmt.Sprintf("read failed: %v", err)
+		log.Printf("[WARN] ValidateDump FAIL: %s — %s", filePath, v.Error)
 		return v
 	}
 
@@ -295,15 +298,18 @@ func ValidateDump(filePath string, dbType DBType) DumpValidation {
 		case DBTypePostgres:
 			v.Error = "PostgreSQL dump missing comment header"
 		}
+		log.Printf("[WARN] ValidateDump FAIL: %s — %s", filePath, v.Error)
 		return v
 	}
 
 	if tableCount == 0 {
 		v.Error = "no CREATE TABLE statements found"
+		log.Printf("[WARN] ValidateDump FAIL: %s — %s (header was found, scanned %d lines)", filePath, v.Error, len(strings.Split(content, "\n")))
 		return v
 	}
 
 	v.Valid = true
+	log.Printf("[DEBUG] ValidateDump OK: %s — %d tables, header found", filePath, tableCount)
 	return v
 }