Minimal self-host fix: dashboard rewrites and NEXT_PUBLIC_API_URL only

[devin-ai-integration]

📥 Pull Request

📘 Description
Fixes dashboard authentication and API communication issues in self-hosted AgentOps deployments by adding necessary environment variable propagation and client-side request proxying.

Changes:

• app/compose.yaml: Pass NEXT_PUBLIC_API_URL to dashboard container at build time and runtime
• app/dashboard/next.config.js: Add rewrites to proxy /auth/* and /opsboard/* requests from dashboard to API server

Problem Solved:
In self-hosted environments, the dashboard was unable to authenticate users or fetch data from the API because it couldn't properly route requests to the local API server.

🧪 Testing

• ⚠️ Limited testing: Verified Docker Compose builds successfully and Next.js config syntax is valid
• Requires human testing: Full authentication flow and dashboard functionality in self-hosted environment

🔍 Human Review Checklist

• CRITICAL: Test complete login/authentication flow works in self-hosted setup
• Verify dashboard can access /auth and /opsboard endpoints through rewrites
• Confirm NEXT_PUBLIC_API_URL environment variable is properly set and accessible
• Test that existing functionality isn't broken by the new rewrites
• Validate in actual self-hosted Docker Compose environment

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Link to Devin run: https://app.devin.ai/sessions/7c733bfe44374472882fafc78a2552b3
Requested by: @areibman

[devin-ai-integration]

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