Add Telegram Web stream downloads

[hongleir2]

Summary

This PR adds support for downloading Telegram Web stream media directly using the --stream flag, without requiring a public/private message URL or a prior message export step.

What gets downloaded

• Media files — Telegram Web stream/... payloads that point to document media such as videos or other files
• Original filenames — uses the fileName value from the stream payload when available

New flags

Flag	Description
--stream <stream_payload>	Download a Telegram Web stream/... payload

Usage & Examples

Download a Telegram Web stream payload:

tdl dl --stream <stream_payload>

# Example
tdl dl --stream 'stream/%7B%22dcId%22%3A1...%7D'

Download multiple stream payloads:

tdl dl --stream <stream_payload_1> --stream <stream_payload_2>

Optional: save to a specific directory:

tdl dl --stream <stream_payload> -d ./downloads

Optional: rewrite the output extension from detected file content:

tdl dl --stream <stream_payload> --rewrite-ext

Notes

Telegram Web stream payloads include temporary file_reference values. If the reference has expired, refresh Telegram Web and copy a fresh stream/... value, or use the original message link when available.

Validation

• go test ./app/dl ./cmd
• Manual verification with valid Telegram Web stream/... payloads saved files to ~/Downloads.