feat: add Go TUI rendering and terminal helper functions

7 funciones Go del dominio tui: apply_gradient (gradiente de color en texto),
draw_box y draw_separator (renderizado de cajas y separadores con box_chars),
load_ascii_art (carga de arte ASCII desde archivos), normalize_terminal_output
y strip_ansi (limpieza de salida de terminal), read_dir_autocomplete
(autocompletado de rutas de directorio). Incluye box_chars.go como helper
de caracteres Unicode para bordes.

functions/tui/load_ascii_art.go

@@ -0,0 +1,52 @@
+package tui
+
+import (
+	"bufio"
+	"math/rand"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+// LoadASCIIArt reads a random .txt file from staticPath and returns it
+// rendered with a color gradient. Pass nil for colors to use DefaultGradientColors.
+// Returns "" if no .txt files are found or on any error.
+func LoadASCIIArt(staticPath string, colors []lipgloss.Color) string {
+	files, err := os.ReadDir(staticPath)
+	if err != nil {
+		return ""
+	}
+
+	var txtFiles []string
+	for _, f := range files {
+		if !f.IsDir() && strings.HasSuffix(f.Name(), ".txt") {
+			txtFiles = append(txtFiles, f.Name())
+		}
+	}
+	if len(txtFiles) == 0 {
+		return ""
+	}
+
+	rng := rand.New(rand.NewSource(time.Now().UnixNano()))
+	selected := txtFiles[rng.Intn(len(txtFiles))]
+
+	file, err := os.Open(filepath.Join(staticPath, selected))
+	if err != nil {
+		return ""
+	}
+	defer file.Close()
+
+	var lines []string
+	sc := bufio.NewScanner(file)
+	for sc.Scan() {
+		lines = append(lines, sc.Text())
+	}
+
+	if len(lines) == 0 {
+		return ""
+	}
+	return ApplyGradient(lines, colors)
+}