feat: initial implementation of uptodownbot

Telegram bot for downloading media from any site using yt-dlp.
Supports audio/video/both, quality selection, language picker,
container format selection, playlist pagination, progress updates,
per-user quotas, user preferences, download history, cancel at any step,
polling and webhook modes, proxy support, and SQLite persistence.

internal/domain/sanitize.go

@@ -0,0 +1,19 @@
+package domain
+
+import (
+	"net/url"
+	"strings"
+)
+
+// ValidateURL checks if the given string is a valid HTTP(S) URL.
+func ValidateURL(raw string) (string, bool) {
+	raw = strings.TrimSpace(raw)
+	if raw == "" {
+		return "", false
+	}
+	u, err := url.Parse(raw)
+	if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
+		return "", false
+	}
+	return raw, true
+}