chore: CLAUDE.md compliance — relative paths, CORS, README tech stack, .vch-description

- Fix absolute API paths in index.html (/analyze, /move, /preview → relative)
- Allow all CORS origins in server.py for reverse-proxy compatibility
- Add tech stack section to README.md
- Create .vch-description for VCH Showcase

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -30,3 +30,11 @@ Der Browser öffnet automatisch http://localhost:8000.
 - **KI-Analyse** — Claude Vision API (optional, ca. 0,003 € / Foto)
 
 Aussortierte Fotos landen in `_aussortiert/` im analysierten Ordner.
+
+## Tech Stack
+
+- **Backend:** Python 3, FastAPI, Uvicorn
+- **Bildanalyse:** OpenCV (Laplacian Variance), Pillow, ImageHash (pHash/MD5)
+- **KI-Analyse (optional):** Anthropic Claude Vision API
+- **Frontend:** Vanilla HTML/CSS/JavaScript (kein Framework)
+- **Konfiguration:** python-dotenv