feat(telegram): support custom base_url for credential proxy

When extra.base_url is set in the Telegram platform config, use it as
the base URL for all Telegram API requests instead of api.telegram.org.
This allows agents to route Telegram traffic through the credential
proxy, which injects the real bot token — the VM never sees it.

Also supports extra.base_file_url for file downloads (defaults to
base_url if not set separately).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

gateway/platforms/telegram.py

@@ -518,6 +518,16 @@ class TelegramAdapter(BasePlatformAdapter):
 
             # Build the application
             builder = Application.builder().token(self.config.token)
+            custom_base_url = self.config.extra.get("base_url")
+            if custom_base_url:
+                builder = builder.base_url(custom_base_url)
+                builder = builder.base_file_url(
+                    self.config.extra.get("base_file_url", custom_base_url)
+                )
+                logger.info(
+                    "[%s] Using custom Telegram base_url: %s",
+                    self.name, custom_base_url,
+                )
 
             # PTB defaults (pool_timeout=1s) are too aggressive on flaky networks and
             # can trigger "Pool timeout: All connections in the connection pool are occupied"
@@ -547,7 +557,6 @@ class TelegramAdapter(BasePlatformAdapter):
                 for k in ("HTTPS_PROXY", "HTTP_PROXY", "ALL_PROXY", "https_proxy", "http_proxy", "all_proxy")
             )
             disable_fallback = (os.getenv("HERMES_TELEGRAM_DISABLE_FALLBACK_IPS", "").strip().lower() in ("1", "true", "yes", "on"))
-
             fallback_ips = self._fallback_ips()
             if not fallback_ips:
                 fallback_ips = await discover_fallback_ips()