chore: remove unused Alacritty duplicates and dead script

Clean up legacy Alacritty theme files and an unreferenced theme-detection script, and fix README links to existing setup docs.

Made-with: Cursor

scripts/detect-system-theme.sh

@@ -1,13 +0,0 @@
-#!/bin/bash
-
-# Detect macOS system theme (light/dark mode)
-# Returns "light" or "dark"
-
-# Get the current appearance setting
-appearance=$(defaults read -g AppleInterfaceStyle 2>/dev/null)
-
-if [ "$appearance" = "Dark" ]; then
-    echo "dark"
-else
-    echo "light"
-fi