fix(telegram): change default replyToMode from "first" to "off"

In 2026.2.13, the combination of implicit reply threading (#14976) and
the existing Telegram default replyToMode="first" causes every bot
response in DMs to be sent as a native Telegram reply (quoted message
bubble), even for simple exchanges like "Hi" → "Hey".

This is a UX regression: prior to 2026.2.13, reply threading was less
consistent so the "first" default rarely produced visible quote bubbles
in DMs. Now that implicit threading works reliably, the default
effectively means every first message in a response gets quoted —
which feels noisy and unexpected in 1:1 conversations.

Changing the default to "off" restores the pre-2026.2.13 DM experience.
Users who want reply threading can still opt in via config:

  channels.telegram.replyToMode: "first" | "all"

Tested by toggling replyToMode on a live 2026.2.13 instance:
- replyToMode="first" → every response quotes the user message
- replyToMode="off" → clean responses without quote bubbles

No test changes needed: existing tests explicitly set replyToMode
rather than relying on the default.

src/telegram/bot.ts

@@ -244,7 +244,7 @@ export function createTelegramBot(opts: TelegramBotOptions) {
       ? telegramCfg.allowFrom
       : undefined) ??
     (opts.allowFrom && opts.allowFrom.length > 0 ? opts.allowFrom : undefined);
-  const replyToMode = opts.replyToMode ?? telegramCfg.replyToMode ?? "first";
+  const replyToMode = opts.replyToMode ?? telegramCfg.replyToMode ?? "off";
   const nativeEnabled = resolveNativeCommandsEnabled({
     providerId: "telegram",
     providerSetting: telegramCfg.commands?.native,