fix: Remove hardcoded ports, support custom port configuration

- Replace all hardcoded localhost:8000/3000/8501 with environment variables
- Frontend: Use API_PORT env var in next.config.ts
- Backend: Use API_PORT env var in editor.py and quality.py
- Web UI: Use API_PORT and EDITOR_PORT env vars in all Streamlit pages
- Update dev.sh to pass environment variables to all services
- Add .env.example with port configuration template

Now supports custom ports via environment variables:
  API_PORT=8080 EDITOR_PORT=3001 WEB_PORT=8502 ./dev.sh

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

api/routers/quality.py

@@ -349,8 +349,9 @@ async def extract_style(
         # Convert URL to file path if needed
         actual_path = image_path
         if image_path.startswith("http"):
-            # Extract path from URL like http://localhost:8000/api/files/...
-            actual_path = image_path.replace("http://localhost:8000/api/files/", "output/")
+            # Extract path from URL (format: http://localhost:{port}/api/files/{relative_path})
+            if "/api/files/" in image_path:
+                actual_path = "output/" + image_path.split("/api/files/")[-1]
         
         # Check if file exists
         import os