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

docs/quickstart.md

@@ -19,17 +19,11 @@ For a more honest snapshot of gaps and current direction, see `docs/status.md`.
 ### 1. Clone
 
 ```bash
-git clone https://github.com/Kelsidavis/WoWee.git
-cd wowee
+git clone --recurse-submodules https://github.com/Kelsidavis/WoWee.git
+cd WoWee
 ```
 
-### 2. Install ImGui
-
-```bash
-git clone https://github.com/ocornut/imgui.git extern/imgui
-```
-
-### 3. Build
+### 2. Build
 
 ```bash
 cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
@@ -96,7 +90,7 @@ Use `BUILD_INSTRUCTIONS.md` for distro-specific package lists.
 
 - Verify auth/world server is running
 - Check host/port settings
-- Check server logs and client logs in `build/bin/logs/`
+- Check server logs and client logs in `logs/wowee.log`
 
 ### Missing assets (models/textures/terrain)