Fixed DC203 Bug
Root cause: When DC 203 is configured via --dc-ip 203:..., the pool's warmup() and refill() methods called connect_ws_for_dc with the raw DC number 203. This caused ws_domains() to construct hostnames like kws203.web.telegram.org — but Telegram's TLS certificate is only valid for *.telegram.org (single-level wildcard), so kws203.web.telegram.org fails TLS verification.
Note: proxy.rs already correctly computed a ws_dc override (203→2) for fresh connections in step 6b, but the pool was never using that override.
Fix: Applied the DC override mapping from default_dc_overrides() directly inside ws_domains() in ws_client.rs. Now when ws_domains(203, ...) is called anywhere (pool warmup, pool refill, fresh connections), it automatically maps 203→2 and constructs valid hostnames like kws2.web.telegram.org.