refactor: update group duty pin functionality and documentation

- Changed the behavior of the group duty pin feature to send a new message, unpin the old one, and pin the new one instead of editing the existing message. This ensures the pinned message is always fresh.
- Updated the `DUTY_PIN_NOTIFY` configuration description in the documentation to reflect the new message handling approach.
- Revised the architecture documentation to clarify the updated group duty pin process.
- Enhanced tests to verify the new behavior of the group duty pin functionality, ensuring proper message handling and scheduling.

duty_teller/handlers/group_duty_pin.py

@@ -94,12 +94,12 @@ async def _schedule_next_update(
 async def _refresh_pin_for_chat(
     context: ContextTypes.DEFAULT_TYPE, chat_id: int
 ) -> Literal["updated", "no_message", "failed"]:
-    """Refresh pinned duty message for a chat: edit text, optionally re-pin, schedule next.
+    """Refresh pinned duty message: send new message, unpin old, pin new, save new message_id.
 
     Returns:
-        "updated" if the message was updated successfully;
+        "updated" if the message was sent, pinned and saved successfully;
         "no_message" if there is no pin record for this chat;
-        "failed" if edit or permissions failed.
+        "failed" if send_message or permissions failed.
     """
     loop = asyncio.get_running_loop()
     message_id = await loop.run_in_executor(None, _sync_get_message_id, chat_id)
@@ -110,28 +110,27 @@ async def _refresh_pin_for_chat(
         None, lambda: _get_duty_message_text_sync(config.DEFAULT_LANGUAGE)
     )
     try:
-        await context.bot.edit_message_text(
-            chat_id=chat_id,
-            message_id=message_id,
-            text=text,
-        )
+        msg = await context.bot.send_message(chat_id=chat_id, text=text)
     except (BadRequest, Forbidden) as e:
-        logger.warning("Failed to edit pinned message chat_id=%s: %s", chat_id, e)
+        logger.warning(
+            "Failed to send duty message for pin refresh chat_id=%s: %s", chat_id, e
+        )
         next_end = await loop.run_in_executor(None, _get_next_shift_end_sync)
         await _schedule_next_update(context.application, chat_id, next_end)
         return "failed"
-    if config.DUTY_PIN_NOTIFY:
-        try:
-            await context.bot.unpin_chat_message(chat_id=chat_id)
-            await context.bot.pin_chat_message(
-                chat_id=chat_id,
-                message_id=message_id,
-                disable_notification=False,
-            )
-        except (BadRequest, Forbidden) as e:
-            logger.warning(
-                "Re-pin after update failed chat_id=%s: %s", chat_id, e
-            )
+    try:
+        await context.bot.unpin_chat_message(chat_id=chat_id)
+        await context.bot.pin_chat_message(
+            chat_id=chat_id,
+            message_id=msg.message_id,
+            disable_notification=not config.DUTY_PIN_NOTIFY,
+        )
+    except (BadRequest, Forbidden) as e:
+        logger.warning("Unpin or pin after refresh failed chat_id=%s: %s", chat_id, e)
+        next_end = await loop.run_in_executor(None, _get_next_shift_end_sync)
+        await _schedule_next_update(context.application, chat_id, next_end)
+        return "failed"
+    await loop.run_in_executor(None, _sync_save_pin, chat_id, msg.message_id)
     next_end = await loop.run_in_executor(None, _get_next_shift_end_sync)
     await _schedule_next_update(context.application, chat_id, next_end)
     return "updated"
@@ -253,9 +252,7 @@ async def pin_duty_cmd(update: Update, context: ContextTypes.DEFAULT_TYPE) -> No
         await update.message.reply_text(t(lang, "pin_duty.failed"))
 
 
-async def refresh_pin_cmd(
-    update: Update, context: ContextTypes.DEFAULT_TYPE
-) -> None:
+async def refresh_pin_cmd(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
     """Handle /refresh_pin: immediately refresh pinned duty message in the group."""
     if not update.message or not update.effective_chat or not update.effective_user:
         return