feat(api): implement OpenAPI/REST API for file conversions

- Add comprehensive REST API at /api/v1 with modular structure
- Implement authentication endpoints (register, login, logout, me)
- Add converter listing and format discovery endpoints
- Create job management and file download endpoints
- Add health check endpoint for monitoring
- Set up CORS support for browser-based API clients
- Create API middleware for JWT authentication
- Add environment variables for API configuration
- Include comprehensive API documentation and test script

Infrastructure:
- Enhanced CI/CD workflow for custom Docker registries
- Docker Compose setup with dev, prod, and monitoring profiles
- Claude.ai integration files for development workflow
- Environment-based configuration with .env.development

Known limitations:
- JWT authentication context needs fixing (using ALLOW_UNAUTHENTICATED=true)
- Swagger UI temporarily disabled due to composition error
- File upload endpoint needs multipart/form-data support

The API code is isolated in src/api/ directory to maintain separation
from the existing codebase, making it easy to maintain or contribute back.

.github/workflows/README.md

@@ -0,0 +1,107 @@
+# GitHub Actions Configuration
+
+This directory contains GitHub Actions workflows for building and publishing Docker images.
+
+## Workflows
+
+### docker-publish.yml (Original)
+The original workflow that publishes to:
+- GitHub Container Registry (ghcr.io)
+- Docker Hub
+
+### docker-publish-custom.yml (Enhanced)
+Enhanced workflow that supports custom Docker registries while maintaining backward compatibility.
+
+## Configuration
+
+To use a custom Docker registry, set the following in your repository:
+
+### Repository Variables (Settings → Secrets and variables → Actions → Variables)
+- `DOCKER_REGISTRY`: Your custom registry URL (e.g., `registry.company.com`)
+- `DOCKER_USERNAME`: Username for custom registry authentication
+- `DOCKERHUB_USERNAME`: Your Docker Hub username (optional)
+- `PUSH_TO_GHCR`: Set to `false` to disable GHCR push (default: `true`)
+- `PUSH_TO_DOCKERHUB`: Set to `true` to enable Docker Hub push (default: `false`)
+- `PUSH_TO_CUSTOM`: Set to `true` to enable custom registry push (default: `false`)
+
+### Repository Secrets (Settings → Secrets and variables → Actions → Secrets)
+- `DOCKER_PASSWORD`: Password/token for custom registry authentication
+- `DOCKERHUB_TOKEN`: Docker Hub access token (if using Docker Hub)
+
+## Usage Examples
+
+### 1. Use only custom registry
+Set variables:
+```
+DOCKER_REGISTRY=registry.mycompany.com
+DOCKER_USERNAME=myuser
+PUSH_TO_CUSTOM=true
+PUSH_TO_GHCR=false
+PUSH_TO_DOCKERHUB=false
+```
+
+Set secrets:
+```
+DOCKER_PASSWORD=<your-registry-password>
+```
+
+### 2. Use custom registry + GHCR
+Set variables:
+```
+DOCKER_REGISTRY=registry.mycompany.com
+DOCKER_USERNAME=myuser
+PUSH_TO_CUSTOM=true
+PUSH_TO_GHCR=true
+PUSH_TO_DOCKERHUB=false
+```
+
+### 3. Use all three registries
+Set variables:
+```
+DOCKER_REGISTRY=registry.mycompany.com
+DOCKER_USERNAME=myuser
+DOCKERHUB_USERNAME=mydockerhubuser
+PUSH_TO_CUSTOM=true
+PUSH_TO_GHCR=true
+PUSH_TO_DOCKERHUB=true
+```
+
+Set secrets:
+```
+DOCKER_PASSWORD=<your-registry-password>
+DOCKERHUB_TOKEN=<your-dockerhub-token>
+```
+
+## Image Tags
+
+The workflow creates the following tags:
+- `latest`: Latest build from main branch
+- `main`: Main branch builds
+- `pr-123`: Pull request builds
+- `v1.2.3`: Semantic version tags
+- `1.2`: Major.minor version
+- `1`: Major version
+- `main-sha-abc123`: SHA-based tags
+
+## Switching Workflows
+
+To switch from the original to the custom workflow:
+
+1. Rename workflows:
+   ```bash
+   mv .github/workflows/docker-publish.yml .github/workflows/docker-publish-original.yml
+   mv .github/workflows/docker-publish-custom.yml .github/workflows/docker-publish.yml
+   ```
+
+2. Or update the workflow triggers to disable one:
+   ```yaml
+   on:
+     workflow_dispatch:  # Manual trigger only
+   ```
+
+## Troubleshooting
+
+1. **Authentication failures**: Check that secrets are correctly set
+2. **Push failures**: Ensure the registry URL doesn't include `https://`
+3. **Missing images**: Verify the PUSH_TO_* variables are set correctly
+4. **Build failures**: Check Docker build logs in the Actions tab