refactor(frontend): app layout and event handler

[amanape]

End-user friendly description of the problem this fixes or functionality that this introduces

• Include this change in the Release Notes. If checked, you must provide an end-user friendly description for your change below

---

Give a summary of what the PR does, explaining any non-trivial design decisions

• Move posthog.capture("user_activated"); capture logic to user prefs context
• Move _oh.app.tsx to _oh.app/route.tsx
• Contain all relevant components within the new _oh.app directory
• Refactor chat-interface.tsx
• Refactor event-handler.tsx into hooks (would like @tofarr's opinions here)

---

Link of any specific issues this addresses

---

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:c370bcf-nikolaik   --name openhands-app-c370bcf   docker.all-hands.dev/all-hands-ai/openhands:c370bcf

[tofarr]

🍰