perf: eliminate per-frame heap allocs in M2 renderer; UI polish and report

M2 renderer: move 3 per-frame local containers to member variables:
- particleGroups_ (unordered_map): reuse bucket structure across frames
- ribbonDraws_ (vector): reuse draw call buffer
- shadowTexSetCache_ (unordered_map): reuse descriptor cache
Eliminates ~3 heap allocations per frame in particle/ribbon/shadow passes.

UI polish:
- Nameplate hover tooltip showing level, class (players), guild name
- Bag window titles show slot counts: "Backpack (12/16)"

Player report: CMSG_COMPLAIN packet builder and reportPlayer() method.
"Report Player" option in target frame right-click menu for other players.
Server response handler (SMSG_COMPLAIN_RESULT) was already implemented.

src/game/game_handler.cpp

@@ -13784,6 +13784,23 @@ void GameHandler::initiateTrade(uint64_t targetGuid) {
     LOG_INFO("Initiated trade with target: 0x", std::hex, targetGuid, std::dec);
 }
 
+void GameHandler::reportPlayer(uint64_t targetGuid, const std::string& reason) {
+    if (!isInWorld()) {
+        LOG_WARNING("Cannot report player: not in world or not connected");
+        return;
+    }
+
+    if (targetGuid == 0) {
+        addSystemChatMessage("You must target a player to report.");
+        return;
+    }
+
+    auto packet = ComplainPacket::build(targetGuid, reason);
+    socket->send(packet);
+    addSystemChatMessage("Player report submitted.");
+    LOG_INFO("Reported player: 0x", std::hex, targetGuid, std::dec, " reason=", reason);
+}
+
 void GameHandler::stopCasting() {
     if (!isInWorld()) {
         LOG_WARNING("Cannot stop casting: not in world or not connected");