docs: remove non-existent WOWEE_EXPANSION env var; fix install snippets

- GETTING_STARTED.md / EXPANSION_GUIDE.md: WOWEE_EXPANSION is not read
  anywhere in src/. Expansion is selected via the auth screen, which
  calls ExpansionRegistry::setActive() (src/ui/auth_screen.cpp:104).
- README.md install snippets: trailing '# comment' on backslash-
  continued lines silently breaks the apt/dnf/pacman command. Moved
  comments above each block.
- README.md Arch snippet: replace vulkan-devel (not a real Arch
  package, per BUILD_INSTRUCTIONS.md:36-38) with vulkan-headers +
  vulkan-icd-loader.

EXPANSION_GUIDE.md

@@ -37,11 +37,10 @@ WoWee auto-detects the expansion based on:
 
 ### Manual Selection
 
-Set environment variable:
-```bash
-WOWEE_EXPANSION=tbc ./wowee    # Force TBC
-WOWEE_EXPANSION=classic ./wowee # Force Classic
-```
+Choose the expansion in the auth/realm screen at launch. The selection
+calls `ExpansionRegistry::setActive(id)` (see `src/ui/auth_screen.cpp`)
+which loads the matching opcode table, update-field layout, and DBC
+layout for that expansion.
 
 ## Key Differences Between Expansions
 

GETTING_STARTED.md

@@ -155,10 +155,7 @@ WoWee auto-detects expansion from server:
 - **TBC 2.4.3** - Burning Crusade
 - **WotLK 3.3.5a** - Wrath of the Lich King
 
-You can override with environment variable:
-```bash
-WOWEE_EXPANSION=tbc ./wowee    # Force TBC
-```
+Pick the expansion from the realm/auth screen at launch — the selection is wired through `ExpansionRegistry::setActive()` (`src/ui/auth_screen.cpp`). There is no `WOWEE_EXPANSION` environment variable.
 
 ## Troubleshooting
 

README.md

@@ -127,34 +127,32 @@ Press Escape to open **Video Settings** and select a preset, or adjust individua
 
 ```bash
 # Ubuntu/Debian
+# Optional packages (libunicorn-dev / libstorm-dev) enable the Warden
+# module executor and the asset_extract tool respectively.
 sudo apt install libsdl2-dev libglm-dev libssl-dev \
                  libvulkan-dev vulkan-tools glslc \
                  libavformat-dev libavcodec-dev libswscale-dev libavutil-dev \
                  zlib1g-dev cmake build-essential libx11-dev \
-                 libunicorn-dev \          # optional: Warden module execution
-                 libstorm-dev              # optional: asset_extract tool
+                 libunicorn-dev libstorm-dev
 
-# Fedora
+# Fedora — unicorn-devel and StormLib-devel are optional (see above)
 sudo dnf install SDL2-devel glm-devel openssl-devel \
                  vulkan-devel vulkan-tools glslc \
                  ffmpeg-devel zlib-devel cmake gcc-c++ libX11-devel \
-                 unicorn-devel \           # optional: Warden module execution
-                 StormLib-devel            # optional: asset_extract tool
+                 unicorn-devel StormLib-devel
 
-# Arch
+# Arch — vulkan-devel is not a real package on Arch; install the
+# headers + loader explicitly. unicorn is optional (Warden);
+# StormLib must be installed from AUR for asset_extract.
 sudo pacman -S sdl2 glm openssl \
-               vulkan-devel vulkan-tools shaderc \
+               vulkan-headers vulkan-icd-loader vulkan-tools shaderc \
                ffmpeg zlib cmake base-devel libx11 \
-               unicorn                    # optional: Warden module execution
-               # StormLib: install from AUR for asset_extract tool
+               unicorn
 
-# macOS (Homebrew)
+# macOS (Homebrew) — unicorn (Warden) and stormlib (asset_extract) are optional
 brew install cmake pkg-config sdl2 glew glm openssl@3 zlib ffmpeg \
              vulkan-loader vulkan-headers shaderc \
-             unicorn \
-             stormlib
-# unicorn is optional (Warden module execution)
-# stormlib is optional (asset_extract tool)
+             unicorn stormlib
 ```
 
 ### Container build