v0.12.4 — 15 bug fixes (CRITICAL/HIGH/MEDIUM)

CRITICAL:
- C1: SetAppBackupBulk data loss + nil map panic (settings.go)
- C2: UpdateStackConfig nil Env map panic (deploy.go)
- C3: ValidateDump missing scanner.Err() check (dbdump.go)

HIGH:
- H1: nextDailyRun DST bug — use time.Date(day+1) not Add(24h)
- H2: Cache Europe/Budapest timezone with sync.Once in scheduler
- H3: settings.save() leaks .tmp file on WriteFile failure
- H4: SetNotificationPrefs nil pointer panic
- H5: appDirSize + getDirSizeBytes ignore Sscanf return value
- H6: getDirSizeBytes has no timeout — add 30s context
- H7: dbdump.go tmpFile not using defer Close
- H8: UpdateCrossDriveStatus misleading comment

MEDIUM:
- M1: Replace custom containsBytes with strings.Contains
- M2: scheduler.Every() validates interval > 0
- M3: executeJob panic recovery now sets LastRun
- M4: logPostStartStatus copies env slice before goroutine
- M5: Cache timezone in web package via getTimezone() sync.Once

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

controller/internal/notify/notifier.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"log"
 	"net/http"
+	"strings"
 	"sync"
 	"time"
 
@@ -314,14 +315,5 @@ func classifyWarning(message string) string {
 }
 
 func contains(s, substr string) bool {
-	return len(s) >= len(substr) && (s == substr || len(s) > 0 && containsBytes(s, substr))
-}
-
-func containsBytes(s, substr string) bool {
-	for i := 0; i <= len(s)-len(substr); i++ {
-		if s[i:i+len(substr)] == substr {
-			return true
-		}
-	}
-	return false
+	return strings.Contains(s, substr)
 }