refactor: remove NVS/CLI config, use mimi_secrets.h as sole configuration method

All configuration is now done exclusively through mimi_secrets.h at build time.
Removed NVS read/write logic, CLI config commands (wifi_set, set_tg_token,
set_api_key, set_model, set_proxy, clear_proxy, set_search_key), and setter
functions from all modules. CLI retains debug/maintenance commands only.
Updated all documentation to reflect the change.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main/telegram/telegram_bot.h

@@ -4,7 +4,6 @@
 
 /**
  * Initialize the Telegram bot.
- * Reads bot token from NVS.
  */
 esp_err_t telegram_bot_init(void);
 
@@ -21,7 +20,3 @@ esp_err_t telegram_bot_start(void);
  */
 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);