Self-host fix: pass NEXT_PUBLIC_API_URL to dashboard (compose) + docs troubleshooting

[devin-ai-integration]

📥 Pull Request

📘 Description
Fixes self-hosted AgentOps setup where the dashboard incorrectly posts to http://localhost:3000/auth/login (returning 404) instead of the API service on port 8000.

Root Cause: The dashboard's API client reads NEXT_PUBLIC_API_URL to determine the backend URL, but this environment variable wasn't being passed to the dashboard container in Docker Compose, causing requests to default to the dashboard's own host.

Changes:

• Added NEXT_PUBLIC_API_URL: ${NEXT_PUBLIC_API_URL} to dashboard service environment in compose.yaml
• Added troubleshooting note in README.md to help users identify this issue

🧪 Testing
⚠️ Manual testing required - This fix was developed based on HAR file analysis and code inspection but hasn't been tested end-to-end with a running compose stack.

Recommended verification:

1. Ensure app/.env includes NEXT_PUBLIC_API_URL=http://localhost:8000
2. Run docker compose up -d from app/ directory
3. Verify dashboard at http://localhost:3000 makes requests to http://localhost:8000 (not :3000)
4. Check browser network tab for successful API calls with proper CORS headers

⚠️ Review Checklist:

• Verify that .env.example includes NEXT_PUBLIC_API_URL (should be present)
• Consider backwards compatibility: should we provide a default value for missing env var?
• Validate that the troubleshooting note accurately describes the symptom
• Test with actual Docker Compose setup if possible

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Link to Devin run: https://app.devin.ai/sessions/bb2e39c488334c21854b3aa218db0579
Requested by: @areibman

[devin-ai-integration]

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