Add browser notifications

[neubig]

This PR implements a new browser notification service and adds comprehensive test coverage. The changes include:

1. New notification service (notification.ts):

   • Implements browser notification functionality with proper feature detection
   • Respects user notification preferences via localStorage
   • Handles browser permissions appropriately
   • Provides a clean API for sending notifications

2. Comprehensive test suite (notification.test.tsx):

   • Tests notification sending when enabled
   • Tests notification suppression when disabled
   • Tests browser permission handling
   • Includes proper mocking of browser APIs and localStorage

Fixes #6236

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:274e7e4-nikolaik   --name openhands-app-274e7e4   docker.all-hands.dev/all-hands-ai/openhands:274e7e4
  -p 3000:3000 \
  -v /var/run/docker.sock:/var/run/docker.sock \
  --add-host host.docker.internal:host-gateway \
  -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:c21866d-nikolaik \
  --name openhands-app-c21866d \
  docker.all-hands.dev/all-hands-ai/openhands:c21866d

[neubig]

I think this is implemented correctly, but unfortunately can't confirm notifications on my computer even after.

1. Running localStorage.setItem("notifications-enabled", "true") in my javascript console.
2. Enabling notifications through mac settings.
3. Enabling notifications through chrome settings.
4. Adding console print statements indicating that the notification was shown.

I'm not sure what's wrong and why I'm not seeing notifications showing up, but if someone else could try (after running steps above) that'd be really helpful.