refactor: show placeholder for DB URL and central server URL fields

Drop the hardcoded dummy fallbacks for Database.URL and
Application.CentralServerURL in loadConfig so these inputs display their
placeholder instead of a pre-filled value. An existing config.toml still
seeds them on re-run via the decode, so real defaults are preserved.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/tui/model.go

@@ -88,13 +88,14 @@ func loadConfig() AppConfig {
 	config.Server.Environment = "production"
 
 	config.Database.Type = "postgres"
-	config.Database.URL = "postgres://usuario:senha@banco:5432/app_dono_db"
 	config.Database.MaxConns = 10
 	config.Database.MinConns = 2
 
 	config.Certificates.DirPath = "/caminho/para/diretorio"
 
-	config.Application.CentralServerURL = "https://servidor:8443"
+	// Database.URL and Application.CentralServerURL are intentionally left empty so the
+	// fields show their placeholder instead of a pre-filled dummy. A real config.toml
+	// (re-run) still seeds them through the decode below.
 
 	_, err := os.Stat("config.toml")
 	if err == nil {