Initial implementation of TuneRipper API backend

- Add Health, Video, and Download controllers with endpoints for health checks, video details, processing, status, results, and simulated downloads
- Implement IVideoService for YouTube URL validation and mock video info
- Add API models for responses and job status tracking
- Configure DI, CORS (BlazorPolicy), OpenAPI, and root metadata endpoint in Program.cs
- Add README with usage, troubleshooting, and development notes
- Minor project file cleanup and encoding fix

TuneRipper.Api/README.md

@@ -0,0 +1,84 @@
+# TuneRipper API
+
+## Quick Start
+
+### Starting the API
+
+**Option 1: Using the start script (Windows)**
+```cmd
+cd TuneRipper.Api
+start-api.bat
+```
+
+**Option 2: Using the start script (Linux/Mac)**
+```bash
+cd TuneRipper.Api
+chmod +x start-api.sh
+./start-api.sh
+```
+
+**Option 3: Manual start**
+```cmd
+cd TuneRipper.Api
+dotnet run
+```
+
+### API Endpoints
+
+Once running, the API will be available at:
+- **HTTPS**: https://localhost:7160
+- **HTTP**: http://localhost:5112
+
+### Testing the API
+
+1. **Start the API** using one of the methods above
+2. **Open the HTTP test file**: `TuneRipper.Api/api-tests.http`
+3. **Run the connectivity tests first** to verify the API is responding
+4. **Use the main API tests** once connectivity is confirmed
+
+### Troubleshooting
+
+#### "This localhost page can't be found" errors:
+
+1. **Check if API is running**:
+   - Look for console output showing "Now listening on: https://localhost:7160"
+   - If not running, start it using the methods above
+
+2. **Try HTTP instead of HTTPS**:
+   - Use `http://localhost:5112` instead of `https://localhost:7160`
+   - Some development environments have HTTPS certificate issues
+
+3. **Trust development certificates** (for HTTPS):
+   ```cmd
+   dotnet dev-certs https --trust
+   ```
+
+4. **Check port availability**:
+   - Make sure ports 7160 and 5112 aren't used by other applications
+   - You can change ports in `Properties/launchSettings.json`
+
+#### HTTP test file variables not working:
+
+1. **Copy job IDs manually**:
+   - Run a POST request to start processing
+   - Copy the `fileName` value from the response
+   - Use it in the manual test sections
+
+2. **Use the troubleshooting section**:
+   - Start with connectivity tests
+   - Use manual GUID replacements if variables fail
+
+### API Documentation
+
+When the API is running, you can access:
+- **Root endpoint**: https://localhost:7160/ (lists available endpoints)
+- **OpenAPI spec**: https://localhost:7160/openapi/v1.json
+- **Health check**: https://localhost:7160/api/health
+
+### Development
+
+The API includes:
+- Automatic reload on code changes (when using `dotnet run`)
+- Detailed logging in the console
+- CORS enabled for Blazor WebAssembly client
+- OpenAPI/Swagger support for API documentation