fix(dwg): correct ODA download URL + dynamic binary path lookup

- Use www.opendesign.com/guestfiles/get URL (no auth required)
- Auto-find and symlink ODA binary after dpkg install
- app.py searches multiple common install paths

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

dwg2dxf-api/app.py

@@ -13,8 +13,14 @@ app = Flask(__name__)
 
 MAX_FILE_SIZE = 100 * 1024 * 1024  # 100 MB
 
-# ODA File Converter installs here on Ubuntu
-ODA_BIN = "/usr/bin/ODAFileConverter"
+# ODA File Converter — try common install paths
+ODA_BIN = "/usr/local/bin/ODAFileConverter"
+for _p in ["/usr/local/bin/ODAFileConverter", "/usr/bin/ODAFileConverter",
+           "/opt/ODAFileConverter/ODAFileConverter",
+           "/opt/oda-file-converter/ODAFileConverter"]:
+    if os.path.isfile(_p):
+        ODA_BIN = _p
+        break
 
 
 @app.route("/health", methods=["GET"])