Step 164: add update checker and installer manifests

editor/src/UpdateChecker.h

@@ -0,0 +1,52 @@
+#pragma once
+// Step 164: Update checker (stub)
+
+#include <string>
+#include <fstream>
+#include <sstream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+struct UpdateInfo {
+    std::string version;
+    std::string url;
+    std::string notes;
+    bool available = false;
+};
+
+class UpdateChecker {
+public:
+    UpdateInfo check(const std::string& updateUrl) {
+        UpdateInfo info;
+        if (updateUrl.empty()) return info;
+        if (startsWith(updateUrl, "file://")) {
+            std::string path = updateUrl.substr(7);
+            std::ifstream in(path);
+            if (!in.is_open()) return info;
+            std::ostringstream ss;
+            ss << in.rdbuf();
+            parseManifest(ss.str(), info);
+            return info;
+        }
+        // Network not implemented; return stub.
+        return info;
+    }
+
+private:
+    static bool startsWith(const std::string& s, const std::string& prefix) {
+        return s.rfind(prefix, 0) == 0;
+    }
+
+    static void parseManifest(const std::string& text, UpdateInfo& out) {
+        try {
+            json j = json::parse(text);
+            out.version = j.value("version", "");
+            out.url = j.value("url", "");
+            out.notes = j.value("notes", "");
+            out.available = !out.version.empty();
+        } catch (...) {
+            out.available = false;
+        }
+    }
+};