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/dbselector.go

@@ -53,7 +53,8 @@ type databaseListMsg struct {
 
 func fetchDatabases(cfg *config.Config, log logger.Logger) tea.Cmd {
 	return func() tea.Msg {
-		ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+		// 60 seconds for database listing - busy servers may be slow
+		ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
 		defer cancel()
 
 		dbClient, err := database.New(cfg, log)