Convert from Homebrew Formulae to Casks for font installation

Formulae can't install to ~/Library/Fonts/ due to Homebrew sandboxing.
Casks have a built-in `font` artifact that handles this automatically.

- Replace Formula/ with Casks/ directory
- Rewrite generator to produce cask files instead of formulae
- Add .ttc (TrueType Collection) support
- Update all tests for cask format
- Update CLI and documentation
- Fonts with no installable files (TTF/OTF/TTC) are skipped

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Casks/font-dirty-clouds.rb

@@ -0,0 +1,14 @@
+# This file was generated by the font folder cleanup script
+# Do not edit this file directly
+# Installs: OTF
+
+cask "font-dirty-clouds" do
+  version "1.0.0"
+  sha256 :no_check
+
+  url "http://clancy.genet-godzilla.ts.net:8085/Fonts/homebrew-fonts/archive/main.tar.gz"
+  name "Dirty Clouds"
+  homepage "http://clancy.genet-godzilla.ts.net:8085/Fonts/homebrew-fonts"
+
+  font "font_files/font-dirty-clouds/otf/dirty-clouds.otf"
+end