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/config.go

@@ -13,7 +13,9 @@ func GenerateConfigTOML(cv ConfigValues) (string, error) {
 	// [server]
 	sb.WriteString("# Server Configuration\n")
 	sb.WriteString("[server]\n")
-	sb.WriteString("port = 8080\n")
+	// Always containerAppPort: the container listens on this port internally; the
+	// user's port is the host-side mapping (see RunAppClienteContainer).
+	sb.WriteString(fmt.Sprintf("port = %d\n", containerAppPort))
 	sb.WriteString(fmt.Sprintf("timeout_seconds = %s\n", cv.Server["timeout"]))
 	sb.WriteString(fmt.Sprintf("environment = %q\n", cv.Server["environment"]))
 	sb.WriteString("\n")