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.