refactor: extract shared proxy-fetch utility from Telegram module

Move makeProxyFetch to src/infra/net/proxy-fetch.ts and add
resolveProxyFetchFromEnv which reads standard proxy env vars
(HTTPS_PROXY, HTTP_PROXY, and lowercase variants) and returns a
proxy-aware fetch via undici's EnvHttpProxyAgent. Telegram re-exports
from the shared location to avoid duplication.

src/telegram/proxy.ts

@@ -1,17 +1 @@
-import { ProxyAgent, fetch as undiciFetch } from "undici";
-
-export function makeProxyFetch(proxyUrl: string): typeof fetch {
-  const agent = new ProxyAgent(proxyUrl);
-  // undici's fetch is runtime-compatible with global fetch but the types diverge
-  // on stream/body internals. Single cast at the boundary keeps the rest type-safe.
-  // Keep proxy dispatching request-scoped. Replacing the global dispatcher breaks
-  // env-driven HTTP(S)_PROXY behavior for unrelated outbound requests.
-  const fetcher = ((input: RequestInfo | URL, init?: RequestInit) =>
-    undiciFetch(input as string | URL, {
-      ...(init as Record<string, unknown>),
-      dispatcher: agent,
-    }) as unknown as Promise<Response>) as typeof fetch;
-  // Return raw proxy fetch; call sites that need AbortSignal normalization
-  // should opt into resolveFetch/wrapFetchWithAbortSignal once at the edge.
-  return fetcher;
-}
+export { makeProxyFetch } from "../infra/net/proxy-fetch.js";