feat: migrate to Next.js for Mini App and enhance project structure

- Replaced the previous webapp with a new Mini App built using Next.js, improving performance and maintainability.
- Updated the `.gitignore` to exclude Next.js build artifacts and node modules.
- Revised documentation in `AGENTS.md`, `README.md`, and `architecture.md` to reflect the new Mini App structure and technology stack.
- Enhanced Dockerfile to support the new build process for the Next.js application.
- Updated CI workflow to build and test the Next.js application.
- Added new configuration options for the Mini App, including `MINI_APP_SHORT_NAME` for improved deep linking.
- Refactored frontend testing setup to accommodate the new structure and testing framework.
- Removed legacy webapp files and dependencies to streamline the project.

tests/test_handlers_group_duty_pin.py

@@ -90,10 +90,12 @@ def test_get_contact_button_markup_empty_username_returns_none():
 
 
 def test_get_contact_button_markup_returns_markup_when_username_set():
-    """_get_contact_button_markup: BOT_USERNAME set -> returns InlineKeyboardMarkup with t.me deep link (startapp=duty)."""
+    """_get_contact_button_markup: BOT_USERNAME set, no short name -> t.me bot link with startapp=duty."""
     from telegram import InlineKeyboardMarkup
 
-    with patch.object(config, "BOT_USERNAME", "MyDutyBot"):
+    with patch.object(config, "BOT_USERNAME", "MyDutyBot"), patch.object(
+        config, "MINI_APP_SHORT_NAME", ""
+    ):
         with patch.object(mod, "t", return_value="View contacts"):
             result = mod._get_contact_button_markup("en")
     assert result is not None
@@ -107,6 +109,21 @@ def test_get_contact_button_markup_returns_markup_when_username_set():
     assert btn.url == "https://t.me/MyDutyBot?startapp=duty"
 
 
+def test_get_contact_button_markup_with_short_name_uses_direct_miniapp_link():
+    """_get_contact_button_markup: MINI_APP_SHORT_NAME set -> direct Mini App URL with startapp=duty."""
+    from telegram import InlineKeyboardMarkup
+
+    with patch.object(config, "BOT_USERNAME", "MyDutyBot"), patch.object(
+        config, "MINI_APP_SHORT_NAME", "DutyApp"
+    ):
+        with patch.object(mod, "t", return_value="View contacts"):
+            result = mod._get_contact_button_markup("en")
+    assert result is not None
+    assert isinstance(result, InlineKeyboardMarkup)
+    btn = result.inline_keyboard[0][0]
+    assert btn.url == "https://t.me/MyDutyBot/DutyApp?startapp=duty"
+
+
 @pytest.mark.asyncio
 async def test_schedule_next_update_job_queue_none_returns_early():
     """_schedule_next_update: job_queue is None -> log and return, no run_once."""