Rewrite development README for in-cluster workflow

[rowan-stein]

User Request

The current README describes a local development workflow (pnpm install, pnpm test, etc.), but all development and testing should happen inside a Kubernetes cluster. The README should describe:

1. Clone agynio/bootstrap_v2 and run the cluster
2. Use devspace dev to develop the service in-cluster
3. Run tests inside the cluster

Specification

README Structure

# docker-runner
## Prerequisites
## Cluster Setup
## Development
## Running Tests
## Troubleshooting

Prerequisites

Tools needed (no local Node.js/pnpm/buf required — they run inside the dev container):

Tool	Version	Purpose
Docker	—	Required by k3d
k3d	v5.x	Local k3s cluster
Terraform	≥ 1.5.0	Provisions infrastructure
kubectl	—	Cluster interaction
DevSpace	—	In-cluster dev workflow

Cluster Setup

• Clone agynio/bootstrap_v2
• Copy stacks/platform/terraform.tfvars.example → terraform.tfvars
• Run ./apply.sh -y (provisions k3d cluster agyn-local, installs Istio + ArgoCD, deploys platform including docker-runner)
• Verify: kubectl get deployment docker-runner -n platform

Development (DevSpace)

• Ensure kubeconfig points to agyn-local
• Run devspace dev from the docker-runner repo
• What happens: ArgoCD sync paused → deployment patched with devcontainer image → file sync → pnpm install → proto:generate → tsx watch (hot reload) → port forward 50051
• Edit locally, changes sync automatically
• Ctrl+C to stop; cleanup hook restores ArgoCD sync

Running Tests

All tests run inside the dev container via devspace enter:

• Unit tests: pnpm test — no Docker needed
• Integration tests (included in pnpm test): require Docker (provided by DinD sidecar in-cluster)
• E2e tests: DOCKER_RUNNER_SHARED_SECRET=change-me pnpm test:e2e — connects to the running gRPC service on localhost:50051

Troubleshooting

Cover: sync timeout, ArgoCD reverting changes, Docker socket not found, port forwarding issues.

Content to Remove

• Old ## Development section (local pnpm commands)
• Old ## Docker section (docker build — handled by CI)