Add ghostty terminal emulator and opencode AI coding agent

- Add ghostty (GPU-accelerated terminal emulator) to casks
- Add opencode (AI coding agent for terminal) to formulas

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

bin/install_homebrew_casks

@@ -13,6 +13,9 @@ install_homebrew
 # Browsers
 brew install --cask eloston-chromium
 
+# Terminal
+brew install --cask ghostty
+
 # Communication
 brew install --cask deepl
 brew install --cask element