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/ui/game_screen.cpp

@@ -4271,6 +4271,8 @@ void GameScreen::renderTargetFrame(game::GameHandler& gameHandler) {
                     gameHandler.addFriend(name);
                 if (ImGui::MenuItem("Ignore"))
                     gameHandler.addIgnore(name);
+                if (ImGui::MenuItem("Report Player"))
+                    gameHandler.reportPlayer(tGuid, "Reported via UI");
             }
             ImGui::Separator();
             if (ImGui::BeginMenu("Set Raid Mark")) {
@@ -12181,6 +12183,17 @@ void GameScreen::renderNameplates(game::GameHandler& gameHandler) {
             if (mouse.x >= nx0 && mouse.x <= nx1 && mouse.y >= ny0 && mouse.y <= ny1) {
                 // Track mouseover for [target=mouseover] macro conditionals
                 gameHandler.setMouseoverGuid(guid);
+                // Hover tooltip: name, level/class, guild
+                ImGui::BeginTooltip();
+                ImGui::TextUnformatted(unitName.c_str());
+                if (isPlayer) {
+                    uint8_t cid = entityClassId(unit);
+                    ImGui::Text("Level %u %s", level, classNameStr(cid));
+                } else if (level > 0) {
+                    ImGui::Text("Level %u", level);
+                }
+                if (!subLabel.empty()) ImGui::TextColored(ImVec4(0.7f,0.7f,0.7f,1.0f), "%s", subLabel.c_str());
+                ImGui::EndTooltip();
                 if (ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
                     gameHandler.setTarget(guid);
                 } else if (ImGui::IsMouseClicked(ImGuiMouseButton_Right)) {