fix(platform/builder): Add heartbeat mechanism

[aarushik93]

The builder eventually looses connection with our websocket backend, after a few minutes of inactivity.
This PR addes a heartbeat mechanism to allow the connection to remain in the background even with no user activitiy.

Changes 🏗️

The frontend sends a ping and backend responds with a pong

Checklist 📋

For code changes:

• I have clearly listed my changes in the PR description
• I have made a test plan
• I have tested my changes according to the test plan:
  • ...

Example test plan

• Create from scratch and execute an agent with at least 3 blocks
• Import an agent from file upload, and confirm it executes correctly
• Upload agent to marketplace
• Import an agent from marketplace and confirm it executes correctly
• Edit an agent from monitor, and confirm it executes correctly

For configuration changes:

• .env.example is updated or already compatible with my changes
• docker-compose.yml is updated or already compatible with my changes
• I have included a list of my configuration changes in the PR description (under Changes)

Examples of configuration changes

• Changing ports
• Adding new services that need to communicate with each other
• Secrets or environment variable changes
• New or infrastructure changes such as databases

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[qodo-merge-pro]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🧪 No relevant tests

🔒 No security concerns identified

⚡ Recommended focus areas for review Error Handling The heartbeat timeout reconnection logic may cause connection flapping if the server is temporarily slow to respond. Consider implementing exponential backoff for reconnection attempts. Race Condition Multiple simultaneous reconnection attempts could occur if heartbeat timeout and onclose handler both trigger reconnects. Consider adding a reconnection state flag. Resource Leak The heartbeat interval and timeout timers should be cleared when the websocket connection is closed or encounters an error to prevent memory leaks.