feat(macos): Alacritty follows system light/dark appearance

New setup — due for review after you run darwin-rebuild switch and
live with it for a few days. See CLAUDE.md (Alacritty) and
assets/alacritty/README.md.

- HM: import active-colors.toml + Catppuccin latte/mocha fragments
- nix-darwin: launchd.user.agents.alacritty-system-theme + PATH helper
- fish: background sync on Darwin; theme.sh no longer rebuilds for Alacritty
- Remove switch-alacritty-theme.sh (sed + darwin-rebuild per toggle)

Made-with: Cursor

scripts/sync-alacritty-theme.sh

@@ -1,31 +1,5 @@
 #!/bin/bash
-
-# Sync Alacritty theme with system theme
-# This script detects the current system theme and updates the theme file that Nix reads
-
+# Back-compat wrapper: sync Alacritty + nvim marker from macOS appearance.
 set -e
-
-# Get the directory where this script is located
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-
-# Paths
-THEME_DETECTION_SCRIPT="$SCRIPT_DIR/detect-system-theme.sh"
-THEME_FILE="/Users/danny/.local/share/nvim_color_scheme"
-
-# Create the directory if it doesn't exist
-mkdir -p "$(dirname "$THEME_FILE")"
-
-# Detect current system theme
-if [ ! -f "$THEME_DETECTION_SCRIPT" ]; then
-    echo "Error: Theme detection script not found at $THEME_DETECTION_SCRIPT"
-    exit 1
-fi
-
-CURRENT_THEME=$("$THEME_DETECTION_SCRIPT")
-echo "Current system theme: $CURRENT_THEME"
-
-# Write the theme to the file that Nix reads
-echo "$CURRENT_THEME" > "$THEME_FILE"
-
-echo "Theme file updated: $THEME_FILE"
-echo "Run 'home-manager switch' to apply the new theme to Alacritty"
+exec "$SCRIPT_DIR/alacritty-sync-system-theme.sh"