Implement technology tree, research queue by least remaining work, and unit/building tech availability & obsolescence

player.h

@@ -2,8 +2,12 @@
 #define PLAYER_H
 
 #include <QString>
+#include <QStringList>
 #include <QColor>
+#include <QMap>
 #include <vector>
+#include <set>
+#include <algorithm>
 
 struct Player {
     int id;
@@ -12,11 +16,17 @@ struct Player {
     QColor secondaryColor;
 
     // National resources (shared across all cities of this nation)
+    // Note: science represents per-tick science generation rate (no longer stockpiled)
     int culture;
     int science;
     int gold;
     int faith;
 
+    // Technology Tree & Research Progression
+    std::set<QString> researchedTechs;
+    QMap<QString, int> techProgress;      // Tech ID -> accumulated science towards that tech
+    std::vector<QString> researchQueue;   // Ordered queue of Tech IDs (front is active research)
+
     Player()
         : id(0), name("Unknown"), primaryColor(Qt::blue), secondaryColor(Qt::white),
           culture(10000), science(0), gold(0), faith(0) {}
@@ -24,6 +34,55 @@ struct Player {
            int pCulture = 10000, int pScience = 0, int pGold = 0, int pFaith = 0)
         : id(pId), name(pName), primaryColor(primary), secondaryColor(secondary),
           culture(pCulture), science(pScience), gold(pGold), faith(pFaith) {}
+
+    bool hasResearched(const QString &techId) const {
+        if (techId.isEmpty()) return true;
+        return researchedTechs.find(techId) != researchedTechs.end();
+    }
+
+    int getTechProgress(const QString &techId) const {
+        return techProgress.value(techId, 0);
+    }
+
+    bool hasActiveResearch() const {
+        return !researchQueue.empty();
+    }
+
+    QString getActiveResearchTech() const {
+        return researchQueue.empty() ? QString() : researchQueue.front();
+    }
+
+    bool isTechQueued(const QString &techId) const {
+        return std::find(researchQueue.begin(), researchQueue.end(), techId) != researchQueue.end();
+    }
+
+    int getTechQueuePosition(const QString &techId) const {
+        for (size_t i = 0; i < researchQueue.size(); ++i) {
+            if (researchQueue[i] == techId) {
+                return static_cast<int>(i) + 1;
+            }
+        }
+        return 0;
+    }
+
+    bool arePrerequisitesMet(const QStringList &prerequisites) const {
+        for (const QString &pre : prerequisites) {
+            if (!hasResearched(pre)) return false;
+        }
+        return true;
+    }
+
+    bool isItemUnlocked(const QString &requiredTech) const {
+        return requiredTech.isEmpty() || hasResearched(requiredTech);
+    }
+
+    bool isItemObsolete(const QString &obsoleteTech) const {
+        return !obsoleteTech.isEmpty() && hasResearched(obsoleteTech);
+    }
+
+    bool isItemBuildable(const QString &requiredTech, const QString &obsoleteTech) const {
+        return isItemUnlocked(requiredTech) && !isItemObsolete(obsoleteTech);
+    }
 };
 
 class PlayerManager {