v3.42.9: Fix all timeout bugs and deadlocks

CRITICAL FIXES:
- Encryption detection false positive (IsBackupEncrypted returned true for ALL files)
- 12 cmd.Wait() deadlocks fixed with channel-based context handling
- TUI timeout bugs: 60s->10min for safety checks, 15s->60s for DB listing
- diagnose.go timeouts: 60s->5min for tar/pg_restore operations
- Panic recovery added to parallel backup/restore goroutines
- Variable shadowing fix in restore/engine.go

These bugs caused pg_dump backups to fail through TUI for months.

internal/tui/backup_exec.go

@@ -83,10 +83,10 @@ type backupCompleteMsg struct {
 
 func executeBackupWithTUIProgress(parentCtx context.Context, cfg *config.Config, log logger.Logger, backupType, dbName string, ratio int) tea.Cmd {
 	return func() tea.Msg {
-		// Use configurable cluster timeout (minutes) from config; default set in config.New()
-		// Use parent context to inherit cancellation from TUI
-		clusterTimeout := time.Duration(cfg.ClusterTimeoutMinutes) * time.Minute
-		ctx, cancel := context.WithTimeout(parentCtx, clusterTimeout)
+		// NO TIMEOUT for backup operations - a backup takes as long as it takes
+		// Large databases can take many hours
+		// Only manual cancellation (Ctrl+C) should stop the backup
+		ctx, cancel := context.WithCancel(parentCtx)
 		defer cancel()
 
 		start := time.Now()