Add local integration testing infrastructure (envtest + kind)

[ian-flores]

Problem

We currently only have unit tests. To test controller behavior against a real Kubernetes API, we deploy to an internal staging cluster. This is slow and risky for iterative development.

Proposed Solution

Implement a two-tier local integration testing strategy:

Tier 1: envtest (fast, API-only)

• Purpose: Test controller reconciliation logic against a real K8s API server (no kubelet)
• Speed: Seconds
• What it tests: Controllers create correct K8s resources (Deployments, Services, ConfigMaps, Secrets) when CRs are applied
• Note: Scaffolding exists in internal/controller/core/suite_test.go but is currently skipped

Tier 2: kind cluster (realistic, full stack)

• Purpose: Test full product deployment with real containers
• Speed: Minutes
• What it tests: Products actually start, health checks pass, ingress works
• Includes: Deploy controller to kind, apply Site CR, verify pods come up healthy

Scope

• Enable envtest suite - Remove Skip(), fix binary path issues, write initial controller reconciliation tests
• Add kind test target - make test-kind that spins up cluster, deploys operator, runs e2e tests
• CI integration - GitHub Actions workflow that runs both tiers
• Developer docs - How to run locally, prerequisites (Docker, kind)

Success Criteria

1. make test runs envtest-based controller tests (fast)
2. make test-kind runs full integration tests against kind (thorough)
3. CI runs both on PRs
4. Live staging cluster used only for final validation

Notes

• envtest already partially scaffolded in suite_test.go
• Consider using chainsaw or similar for declarative e2e tests
• May need mock/stub external dependencies (AWS Secrets Manager, etc.)