fix(native_bridge): strip query string in fx-gui HTTP path + walkthrough notes

- readRequest now trims '?t=<ms>' cache-buster so /frame?t=... matches
  /frame route (frontend VstGuiEmbed polls with timestamp → was 404, no image)
- document: jpeg62.dll manual copy, add auto-opens GUI (already_running
  expected), reopen needs bridge exit wait

native_bridge/src/FxGuiServer.cpp

@@ -22,10 +22,10 @@
 #include <ws2tcpip.h>
 #pragma comment(lib, "ws2_32.lib")
 
+#include <cstdio>
 #include <jpeglib.h>
 
 #include <atomic>
-#include <cstdio>
 #include <cstring>
 #include <functional>
 #include <iostream>
@@ -39,6 +39,12 @@
 namespace {
 
 // --- tiny JSON helpers (same API as RenderFxJob.cpp) ------------------------
+const json_object_element_s* member(const json_object_s* o, const char* key) {
+    for (const json_object_element_s* e = o ? o->start : nullptr; e; e = e->next)
+        if (e->name && e->name->string && std::strcmp(e->name->string, key) == 0)
+            return e;
+    return nullptr;
+}
 const json_value_s* memberValue(const json_object_s* o, const char* key) {
     const json_object_element_s* m = member(o, key);
     return m ? m->value : nullptr;
@@ -83,6 +89,9 @@ bool readRequest(SOCKET c, HttpReq& out) {
     if (sp1 == std::string::npos || sp2 == std::string::npos) return false;
     out.method = head.substr(0, sp1);
     out.path = head.substr(sp1 + 1, sp2 - sp1 - 1);
+    // strip query string: frontend cache-busts /frame?t=<ms>
+    const size_t q = out.path.find('?');
+    if (q != std::string::npos) out.path.resize(q);
 
     long contentLength = 0;
     size_t pos = 0;
@@ -285,7 +294,7 @@ void runHttpServer(HWND hwnd, std::atomic<bool>& stop) {
         } else if (req.path == "/close") {
             sendResponse(c, 200, "application/json", "{\"ok\":true}", 11);
             stop.store(true);
-            PostMessageA(hwnd, WM_CLOSE);  // pump exits -> process returns
+            PostMessageA(hwnd, WM_CLOSE, 0, 0);  // pump exits -> process returns
         } else {
             sendResponse(c, 404, "application/json", "{\"error\":\"not found\"}", 22);
         }