feat: unify theme switching with cross-platform script

- Create unified theme.sh script that works on both WSL and macOS
- Update fish alias to use new unified script instead of WSL-specific one
- Maintain backward compatibility with existing theme command
- Update documentation to reflect unified approach
- Script automatically detects platform and calls appropriate functionality

scripts/theme.sh

@@ -0,0 +1,98 @@
+#!/bin/bash
+
+# Unified theme switching script for WSL and macOS
+# This script handles theme switching for both platforms
+
+set -e
+
+color_scheme=$1
+
+# Validate user input
+if [[ "$color_scheme" != "dark" && "$color_scheme" != "light" ]]; then
+  echo "Usage: theme {dark|light}"
+  echo ""
+  echo "This command switches themes for:"
+  echo "  - Neovim (via nvim_color_scheme file)"
+  echo "  - Alacritty (via Nix configuration on macOS)"
+  echo "  - Windows Terminal (via settings.json on WSL)"
+  echo "  - Windows system theme (on WSL)"
+  exit 1
+fi
+
+# Get the directory where this script is located
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+DOTFILES_DIR="$(dirname "$SCRIPT_DIR")"
+
+# Write theme to nvim color scheme file (works on both platforms)
+nvim_color_theme_path=~/.local/share/nvim_color_scheme
+mkdir -p "$(dirname "$nvim_color_theme_path")"
+echo "$color_scheme" > "$nvim_color_theme_path"
+echo "Updated Neovim theme: $color_scheme"
+
+# Detect platform and handle platform-specific theme switching
+if [[ -n "$WSL_DISTRO_NAME" ]]; then
+  # WSL platform - handle Windows Terminal and system theme
+  echo "Detected WSL platform"
+  
+  # Check that all relevant files exist
+  windows_username=$(powershell.exe '$env:UserName' | tr -d '\r\n')
+  windows_terminal_settings_path="/mnt/c/Users/${windows_username}/AppData/Local/Packages/Microsoft.WindowsTerminal_8wekyb3d8bbwe/LocalState/settings.json"
+  dark_mode_config_path="$DOTFILES_DIR/assets/windows_terminal/dark.settings.json"
+  light_mode_config_path="$DOTFILES_DIR/assets/windows_terminal/light.settings.json"
+
+  if [ ! -f "$light_mode_config_path" ]; then
+    echo "error: light_mode_config_path missing"
+    echo "expected: $light_mode_config_path"
+    exit 1
+  fi
+
+  if [ ! -f "$dark_mode_config_path" ]; then
+    echo "error: dark_mode_config_path missing"
+    echo "expected: $dark_mode_config_path"
+    exit 1
+  fi
+
+  if [ ! -f "$windows_terminal_settings_path" ]; then
+    echo "error: windows terminal settings path missing"
+    echo "expected: $windows_terminal_settings_path"
+    exit 1
+  fi
+
+  # Update Windows Terminal settings
+  if [ "$color_scheme" = 'dark' ]; then
+    cp "$dark_mode_config_path" "$windows_terminal_settings_path"
+    echo "Updated Windows Terminal: dark theme"
+    echo "Switching Windows system theme to dark..."
+    powershell.exe -Command "start C:\Windows\Resources\Themes\dark.theme"
+    powershell.exe "timeout /t 3; taskkill /im systemsettings.exe /f"
+  else
+    cp "$light_mode_config_path" "$windows_terminal_settings_path"
+    echo "Updated Windows Terminal: light theme"
+    echo "Switching Windows system theme to light..."
+    powershell.exe -Command "start C:\Windows\Resources\Themes\aero.theme"
+    powershell.exe "timeout /t 3; taskkill /im systemsettings.exe /f"
+  fi
+
+  echo "Setting Sound Schema to None"
+  powershell.exe -Command "Set-ItemProperty -Path HKCU:\AppEvents\Schemes -Name '(Default)' -Value '.None'"
+
+elif [[ "$OSTYPE" == "darwin"* ]]; then
+  # macOS platform - handle Alacritty theme
+  echo "Detected macOS platform"
+  
+  # Use the existing Alacritty theme switching script
+  alacritty_script="$DOTFILES_DIR/scripts/switch-alacritty-theme.sh"
+  if [ -f "$alacritty_script" ]; then
+    echo "Switching Alacritty theme to: $color_scheme"
+    "$alacritty_script" "$color_scheme"
+  else
+    echo "Warning: Alacritty theme script not found at $alacritty_script"
+    echo "Theme file updated, but Alacritty theme not switched"
+  fi
+
+else
+  # Other platforms - just update the theme file
+  echo "Detected other platform - only updating Neovim theme file"
+fi
+
+echo "Theme switching complete: $color_scheme"