feat: enhance group duty pin command functionality

- Updated the `pin_duty_cmd` to handle cases where no message ID is found by sending a new duty message, pinning it, saving the pin, and scheduling the next update.
- Improved error handling for message sending and pinning operations, providing appropriate replies based on success or failure.
- Enhanced unit tests to cover the new behavior, ensuring proper functionality and error handling in various scenarios.

webapp/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "duty-teller-webapp",
+  "type": "module",
+  "scripts": {
+    "test": "vitest run",
+    "test:watch": "vitest"
+  },
+  "devDependencies": {
+    "happy-dom": "^15.0.0",
+    "vitest": "^2.0.0"
+  }
+}