viewer/curl: keep <curl/curl.h> out of JFJochHttpReader.h (MSVC build fix)

curl.h transitively includes <windows.h>, whose min/max/ERROR/LoadImage
macros clobbered every viewer TU that includes this widely-used header
(std::min/max in gemmi, the TaskState::ERROR enum, the LoadImage() calls,
the Qt/fftw cascade). It even broke JFJochHttpReader.cpp itself, since inside
the header curl.h preceded the reader/common includes that pull in gemmi.

Forward-declare the opaque easy handle (CURL is `typedef void` in libcurl)
so the header no longer needs curl.h, and include curl.h only in the .cpp,
last, after all std/project headers.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

viewer/JFJochHttpReader.cpp

@@ -3,7 +3,6 @@
 
 #include "JFJochHttpReader.h"
 
-#include <curl/curl.h>
 #include <cstring>
 #include <mutex>
 #include <nlohmann/json.hpp>
@@ -15,6 +14,10 @@
 #include "../common/JFJochMath.h"
 #include "../image_analysis/bragg_integration/CalcISigma.h"
 
+// Included last, after all std/project headers: on Windows <curl/curl.h> pulls in <windows.h>,
+// whose min/max (and other) macros must not precede the headers that use std::min / std::max.
+#include <curl/curl.h>
+
 namespace {
     // libcurl write callback: append the received bytes to a std::string (which holds binary fine).
     size_t AppendToString(char *ptr, size_t size, size_t nmemb, void *userdata) {

viewer/JFJochHttpReader.h

@@ -3,13 +3,18 @@
 
 #pragma once
 
-#include <curl/curl.h>
-
 #include "../reader/JFJochReader.h"
 #include "../common/BrokerStatus.h"
 #include "../common/ImageBuffer.h"
 #include "../common/ROIDefinition.h"
 
+// libcurl's easy handle, kept opaque here so this widely-included header does NOT pull in
+// <curl/curl.h>. On Windows curl.h drags in <windows.h>, whose min/max/ERROR/LoadImage macros
+// would then clobber every viewer translation unit that includes this header (breaking std::min /
+// std::max in gemmi, the `ERROR` enum, the LoadImage() calls, ...). CURL is `typedef void` in
+// libcurl; <curl/curl.h> is included only in JFJochHttpReader.cpp.
+using CURL = void;
+
 class JFJochHttpReader : public JFJochReader {
     mutable std::mutex http_mutex;
     std::string addr;