Modifies the Telegram bot's 'Add User' functionality.
After adding a user, the bot now attempts to retrieve and display
the Normal-SUB subscription link and its QR code if available.
If Normal-SUB is not found, it falls back to showing the direct
Hysteria2 IPv4 URI and QR code. The direct URI is also provided as a
fallback if Normal-SUB is shown.
Usernames are quoted in CLI calls
for robustness. Improved input validation for username, traffic,
and expiration days.
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