feat: add group duty pin notification feature

- Introduced a new configuration option `DUTY_PIN_NOTIFY` to control whether the bot re-pins the duty message when updated, providing notifications to group members.
- Updated the architecture documentation to reflect the new functionality of re-pinning duty messages.
- Enhanced the `.env.example` file to include the new configuration option with a description.
- Added tests to verify the behavior of the new refresh pin command and its integration with the existing group duty pin functionality.
- Updated internationalization messages to include help text for the new `/refresh_pin` command.

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+
+- **Group duty pin**: when the pinned duty message is updated on schedule, the bot re-pins it so group members get a Telegram notification. Configurable via `DUTY_PIN_NOTIFY` (default: enabled); set to `0` or `false` to only edit the message without re-pinning.
+
 ## [0.1.0] - 2025-02-20
 
 ### Added