refactor: clarify fixed container port with containerAppPort constant

The container always listens on 8080 internally while the user-provided
port is only the host-side mapping. Make this explicit without changing
behavior or the generated config:

- add a named containerAppPort constant and use it in both the docker -p
  mapping and the config.toml generation (was a bare 8080 literal in two
  places)
- document why config.toml hardcodes the port, so it isn't "fixed" back
  to the form value
- relabel the form field to "Porta (host)"

The generated config.toml is byte-identical (port = 8080).

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

internal/tui/docker.go

@@ -11,6 +11,10 @@ import (
 
 const networkName = "app-dono_app"
 
+// containerAppPort is the port the app cliente container listens on internally.
+// The user-provided port is only the host-side mapping (<host port>:containerAppPort).
+const containerAppPort = 8080
+
 func RunContainer(image string, name string, port int) error {
 
 	cmd := exec.Command(
@@ -123,7 +127,7 @@ func RunAppClienteContainer(image, containerName, configPath, configDestinationP
 	args := []string{
 		"run", "-d",
 		"-u", uidGid,
-		"-p", fmt.Sprintf("%s:8080", cv.Server["port"]),
+		"-p", fmt.Sprintf("%s:%d", cv.Server["port"], containerAppPort),
 		"--name", containerName,
 		"--network", networkName,
 		"--restart", "unless-stopped",