Add HsnTsnClient and related classes for vehicle data scraping

- Implement HsnTsnClient to fetch vehicle data from hsn-tsn.de
- Create VehicleDetail and HsnTsnVehicle classes for data representation
- Add CSV output functionality in Program.cs
- Include necessary NuGet packages in project file
- Add README with usage instructions

README.md

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+# hsntsn-scraper
+
+.NET console scraper.
+
+Kaynak: `http://www.hsn-tsn.de/`
+
+CSV cikti alanlari:
+
+- `HsnTsn`, `Hsn`, `Tsn`
+- `Brand`, `VehicleType`, `Model`, `OfficialType`
+- `YearFrom`, `YearTo`
+- `PowerPs`, `PowerKw`, `DisplacementCcm`, `FuelType`
+- `MatchKey`
+- `SourceQuery`, `SourceListUrl`, `SourceDetailUrl`
+
+## Calistirma
+
+Tum marka sayfalarini tara:
+
+```bash
+dotnet run --project src/HsnTsnScraper/HsnTsnScraper.csproj > hsntsn.csv
+```
+
+Sadece verilen sorgulari tara (`stdin`):
+
+```bash
+printf "0588\nGolf\n" | dotnet run --project src/HsnTsnScraper/HsnTsnScraper.csproj > hsntsn.csv
+```
+
+Detay sayfasi zenginlestirmesini kapat:
+
+```bash
+printf "0588\n" | dotnet run --project src/HsnTsnScraper/HsnTsnScraper.csproj -- --skip-details
+```