Temp: add debug headers route to diagnose ProxyFix scheme detection

Will be removed once the proto-forwarding issue is diagnosed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backoffice/app/app.py

@@ -84,6 +84,11 @@ def rows_json(rows):
     return [{k: jsonable(v) for k, v in r.items()} for r in rows]
 
 
+@app.get("/owner/_debug_headers")
+def _debug_headers():
+    return jsonify({"scheme": request.scheme, "headers": dict(request.headers)})
+
+
 @app.get("/healthz")
 def healthz():
     try: