feat: custom zone discovery system for client auto-detection

- CustomZoneDiscovery scans directories for zone.json manifest files
- Discovers custom zones in custom_zones/ and output/ directories
- Reports: name, author, description, creature/quest availability
- Client can list all available custom expansions at startup
- Foundation for a zone selection menu in the client UI

include/pipeline/custom_zone_discovery.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <string>
+#include <vector>
+#include <cstdint>
+
+namespace wowee {
+namespace pipeline {
+
+struct CustomZoneInfo {
+    std::string name;
+    std::string author;
+    std::string description;
+    std::string directory;
+    uint32_t mapId = 9000;
+    std::vector<std::pair<int, int>> tiles;
+    bool hasCreatures = false;
+    bool hasQuests = false;
+};
+
+class CustomZoneDiscovery {
+public:
+    // Scan directories for custom zones (checks for zone.json files)
+    static std::vector<CustomZoneInfo> scan(const std::vector<std::string>& searchPaths);
+
+    // Scan a single directory
+    static std::vector<CustomZoneInfo> scanDirectory(const std::string& path);
+};
+
+} // namespace pipeline
+} // namespace wowee