feat: initialize warpbox.dev project structure and backend

Initialize the repository with the core Go backend architecture and a frontend mockup for warpbox.dev, a self-hosted file-sharing application.

- Set up Go backend modules for configuration, HTTP server, middleware, handlers, and templates.
- Add local development scripts, environment templates, and basic project configuration.
- Include a React-based frontend mockup under the docs directory.

backend/libs/config/config.go

@@ -0,0 +1,118 @@
+package config
+
+import (
+	"fmt"
+	"math"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+)
+
+type Config struct {
+	AppName       string
+	Environment   string
+	Addr          string
+	BaseURL       string
+	StaticDir     string
+	TemplateDir   string
+	ReadTimeout   time.Duration
+	WriteTimeout  time.Duration
+	IdleTimeout   time.Duration
+	MaxUploadSize int64
+}
+
+func Load() (Config, error) {
+	cfg := Config{
+		AppName:       envString("WARPBOX_APP_NAME", "warpbox.dev"),
+		Environment:   envString("WARPBOX_ENV", "development"),
+		Addr:          envString("WARPBOX_ADDR", ":8080"),
+		BaseURL:       strings.TrimRight(envString("WARPBOX_BASE_URL", "http://localhost:8080"), "/"),
+		StaticDir:     envString("WARPBOX_STATIC_DIR", defaultPath("static")),
+		TemplateDir:   envString("WARPBOX_TEMPLATE_DIR", defaultPath("templates")),
+		ReadTimeout:   envDuration("WARPBOX_READ_TIMEOUT", 15*time.Second),
+		WriteTimeout:  envDuration("WARPBOX_WRITE_TIMEOUT", 60*time.Second),
+		IdleTimeout:   envDuration("WARPBOX_IDLE_TIMEOUT", 120*time.Second),
+		MaxUploadSize: envMegabytes("WARPBOX_MAX_UPLOAD_SIZE_MB", 2048), // 2 GiB default.
+	}
+
+	if cfg.BaseURL == "" {
+		return Config{}, fmt.Errorf("WARPBOX_BASE_URL cannot be empty")
+	}
+	if cfg.MaxUploadSize <= 0 {
+		return Config{}, fmt.Errorf("WARPBOX_MAX_UPLOAD_SIZE_MB must be positive")
+	}
+
+	return cfg, nil
+}
+
+func defaultPath(name string) string {
+	candidates := []string{
+		filepath.Join("backend", name),
+		name,
+	}
+
+	for _, candidate := range candidates {
+		if info, err := os.Stat(candidate); err == nil && info.IsDir() {
+			return candidate
+		}
+	}
+
+	return filepath.Join("backend", name)
+}
+
+func envString(key, fallback string) string {
+	if value := strings.TrimSpace(os.Getenv(key)); value != "" {
+		return value
+	}
+	return fallback
+}
+
+func envDuration(key string, fallback time.Duration) time.Duration {
+	value := strings.TrimSpace(os.Getenv(key))
+	if value == "" {
+		return fallback
+	}
+
+	parsed, err := time.ParseDuration(value)
+	if err != nil {
+		return fallback
+	}
+	return parsed
+}
+
+func envMegabytes(key string, fallback float64) int64 {
+	value := strings.TrimSpace(os.Getenv(key))
+	if value == "" {
+		return megabytesToBytes(fallback)
+	}
+
+	parsed, err := parseMegabytes(value)
+	if err != nil {
+		return megabytesToBytes(fallback)
+	}
+	return parsed
+}
+
+func parseMegabytes(value string) (int64, error) {
+	normalized := strings.TrimSpace(value)
+	normalized = strings.TrimSuffix(normalized, "MB")
+	normalized = strings.TrimSuffix(normalized, "Mb")
+	normalized = strings.TrimSuffix(normalized, "mb")
+	normalized = strings.TrimSpace(normalized)
+
+	sizeMB, err := strconv.ParseFloat(normalized, 64)
+	if err != nil {
+		return 0, fmt.Errorf("invalid megabyte value %q: %w", value, err)
+	}
+	if sizeMB <= 0 {
+		return 0, fmt.Errorf("megabyte value must be positive")
+	}
+
+	return megabytesToBytes(sizeMB), nil
+}
+
+func megabytesToBytes(sizeMB float64) int64 {
+	return int64(math.Round(sizeMB * 1024 * 1024))
+}