Update configuration and access control for Telegram miniapp

- Added ALLOWED_USERNAMES and ADMIN_USERNAMES to .env.example for user access control.
- Implemented validation of Telegram Web App initData in a new telegram_auth.py module.
- Enhanced API to check user access before fetching duties.
- Updated README with instructions for configuring miniapp access.
- Modified .dockerignore and .gitignore to include data directory and database files.

webapp/style.css

@@ -150,3 +150,22 @@ body {
 .error[hidden], .loading.hidden {
   display: none !important;
 }
+
+.access-denied {
+  text-align: center;
+  padding: 24px 12px;
+  color: var(--muted);
+}
+
+.access-denied p {
+  margin: 0 0 8px 0;
+}
+
+.access-denied p:first-child {
+  color: #f7768e;
+  font-weight: 600;
+}
+
+.access-denied[hidden] {
+  display: none !important;
+}