Add Docker build workflow with GitHub Actions

[depadeto]

Context

We need a CI pipeline that builds and validates the project on every PR.

Task

Create .github/workflows/ci.yml that:

• Runs on every PR to main
• Builds all Go services (smart-router, function-manager, tenant-manager, config-store, deployment-manager)
• Builds the Python SkyPilot Bridge (lint + type check)
• Builds the React frontend (npm ci && npm run build)
• Runs any existing tests

Bonus

• Add Docker image builds (don't push, just validate they build)
• Add Go linting with golangci-lint

Good first issue — standard GitHub Actions setup.

[rangampallysonali]

Hi, I’d like to work on this issue.

I’ll add a GitHub Actions CI workflow that:

• runs on pull requests to main
• builds all Go services
• runs lint/type checks for the Python SkyPilot Bridge
• builds the React frontend
• runs existing tests if available
• optionally validates Docker image builds

Please assign this to me.