Update Development Setup Documentation

[ashmortar]

Description

Add runner development setup to existing or new development documentation, showing how to run the control plane and runners locally for testing.

Scope

Create or update docs/development.md with local development setup instructions that include the runner architecture.

Content to Add:

1. Running Eph Locally

## Running Eph Locally

### Control Plane (ephd)

```bash
# Start PostgreSQL
docker run -d -p 5432:5432 \
  -e POSTGRES_PASSWORD=eph \
  -e POSTGRES_DB=eph \
  postgres:16

# Run migrations
go run ./cmd/migrate up

# Start ephd
go run ./cmd/ephd

Runner

# In another terminal
export EPH_TOKEN=dev-token
export EPH_CONTROL_PLANE=http://localhost:8080

go run ./cmd/eph-runner

Testing Full Flow

1. Create a test repo with eph.yaml
2. Open PR and add 'preview' label
3. Watch runner logs for reconciliation
4. Verify namespace created in cluster

#### 2. Environment Variables
Document all required environment variables for local development:
- `EPH_TOKEN` - Runner authentication token
- `EPH_CONTROL_PLANE` - Control plane URL
- `DATABASE_URL` - PostgreSQL connection string
- `GITHUB_APP_ID` - GitHub App ID
- `GITHUB_PRIVATE_KEY` - GitHub App private key

#### 3. Docker Compose Setup
```markdown
### Docker Compose (Alternative)

For a complete local setup:

```yaml
version: '3.8'
services:
  postgres:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: eph
      POSTGRES_DB: eph
    ports:
      - "5432:5432"
  
  ephd:
    build: .
    command: ./ephd
    environment:
      DATABASE_URL: postgres://postgres:eph@postgres:5432/eph
    ports:
      - "8080:8080"
    depends_on:
      - postgres

#### 4. Testing Configuration
Include instructions for:
- Creating test eph.yaml files
- Mocking GitHub webhook events
- Testing runner reconciliation
- Debugging common issues

#### 5. IDE Setup
Include VSCode/GoLand configuration for debugging both ephd and runners.

## Files to Create/Modify
- `docs/development.md` - Local development setup (create if doesn't exist)
- `docker-compose.dev.yml` - Optional development docker-compose file

## Acceptance Criteria
- [ ] Clear instructions for running ephd locally
- [ ] Runner development setup documented
- [ ] Environment variables clearly listed
- [ ] Docker Compose alternative provided
- [ ] Testing flow documented
- [ ] Common development issues addressed
- [ ] IDE debugging setup included

## Labels
`documentation`, `enhancement`

## Phase
1-Documentation

## Priority  
P1 (Medium)