feat: add Telegram bot with long polling and message splitting

Direct HTTPS long polling against Telegram Bot API (getUpdates),
JSON parsing with cJSON, auto-split at 4096 chars, Markdown
with plain-text fallback.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

main/telegram/telegram_bot.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "esp_err.h"
+
+/**
+ * Initialize the Telegram bot.
+ * Reads bot token from NVS.
+ */
+esp_err_t telegram_bot_init(void);
+
+/**
+ * Start the Telegram polling task (long polling on Core 0).
+ */
+esp_err_t telegram_bot_start(void);
+
+/**
+ * Send a text message to a Telegram chat.
+ * Automatically splits messages longer than 4096 chars.
+ * @param chat_id  Telegram chat ID (numeric string)
+ * @param text     Message text (supports Markdown)
+ */
+esp_err_t telegram_send_message(const char *chat_id, const char *text);
+
+/**
+ * Save the Telegram bot token to NVS.
+ */
+esp_err_t telegram_set_token(const char *token);