feat(telegram): add linkPreview config option

Add channels.telegram.linkPreview config to control whether link previews
are shown in outbound messages. When set to false, uses Telegram's
link_preview_options.is_disabled to suppress URL previews.

- Add linkPreview to TelegramAccountConfig type
- Add Zod schema validation for linkPreview
- Pass link_preview_options to sendMessage in send.ts and bot/delivery.ts
- Propagate linkPreview config through deliverReplies callers
- Add tests for link preview behavior

Fixes #1675

Co-Authored-By: Claude <noreply@anthropic.com>

src/telegram/bot-message-dispatch.ts

@@ -151,6 +151,7 @@ export const dispatchTelegramMessage = async ({
           tableMode,
           chunkMode,
           onVoiceRecording: sendRecordVoice,
+          linkPreview: telegramCfg.linkPreview,
         });
       },
       onError: (err, info) => {