v2.4.9: UBF v2.0 backup + manual secret recovery

- lib/backup.sh: complete rewrite for Unified Backup Format v2.0
  * metadata.json with backup_id (GT-YYMMDD-<last6hex>) and SHA-256 fingerprint
  * secrets.json with raw_secret, faketls_secret, proxy_link, bot_token
  * structured dirs: telemt/, gotelegram/, nginx/, letsencrypt/, site/, bot/
  * auto-detect and auto-migrate v1.1 -> v2.0 on restore
  * parse_manual_secret: accepts tg://proxy URL, ee-prefix, or raw 32-hex
  * manual_secret_input: interactive entry with env var export
- install.sh: new 3-option menu_install (new / restore / existing key)
  * install_lite_mode + install_pro_mode respect GOTELEGRAM_EXISTING_* env vars
- lib/lang/ru.sh + en.sh: v2.4.9 i18n strings (backup_*, manual_secret_*, install_menu_*)
- lib/common.sh + gotelegram-bot/bot.py: version bump to 2.4.9

gotelegram-bot/bot.py

@@ -100,7 +100,7 @@ logger = logging.getLogger(__name__)
 # CONFIGURATION
 # ============================================================================
 
-GOTELEGRAM_VERSION = "2.4.8"
+GOTELEGRAM_VERSION = "2.4.9"
 GOTELEGRAM_CONFIG = "/opt/gotelegram/config.json"
 TELEMT_CONFIG = "/etc/telemt/config.toml"
 TELEMT_SERVICE = "telemt"