docs: fix stale references across 10 documentation files

- CONTRIBUTING.md: C++17 → C++20 (matches CMakeLists.txt)
- TROUBLESHOOTING.md: fix log path (~/.wowee/logs/ → logs/wowee.log)
- docs/authentication.md: remove stale "next milestone" (char enum
  and world entry have been working for months)
- docs/srp-implementation.md: update session key status (RC4 encryption
  is implemented), fix file reference to actual src/auth/srp.cpp
- docs/packet-framing.md: remove stale "next steps" (realm list is
  fully implemented), update status with tested servers
- docs/WARDEN_IMPLEMENTATION.md: fix file list — handler is in
  warden_handler.cpp not game_handler.cpp, add warden_memory.hpp/cpp
- docs/WARDEN_QUICK_REFERENCE.md: fix header/source paths (include/
  not src/), add warden_handler and warden_memory
- docs/quickstart.md: fix clone command (--recurse-submodules, WoWee
  not wowee), remove obsolete manual ImGui clone step, fix log path
- docs/server-setup.md: update version to v1.8.9-preview, date to
  2026-03-30, add all supported expansions
- assets/textures/README.md: remove broken doc references
  (TURTLEHD_IMPORT.md, TEXTURE_MANIFEST.txt), update integration
  status to reflect working PNG override pipeline

TROUBLESHOOTING.md

@@ -151,9 +151,7 @@ Graphics Preset: HIGH or ULTRA
 ## Getting Help
 
 ### Check Logs
-Detailed logs are saved to:
-- **Linux/macOS**: `~/.wowee/logs/`
-- **Windows**: `%APPDATA%\wowee\logs\`
+Detailed logs are saved to `logs/wowee.log` in the working directory (typically `build/bin/`).
 
 Include relevant log entries when reporting issues.