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>

tests/conftest.py

@@ -3,10 +3,10 @@ from pathlib import Path
 
 import pytest
 
-# Repo root: directory containing font_files/ and Formula/
+# Repo root: directory containing font_files/ and Casks/
 REPO_ROOT = Path(__file__).resolve().parent.parent
 FONT_FILES_DIR = REPO_ROOT / "font_files"
-FORMULA_DIR = REPO_ROOT / "Formula"
+CASKS_DIR = REPO_ROOT / "Casks"
 
 REQUIRED_SUBDIRS = ("ttf", "otf", "web", "other_files")
 WEB_EXTENSIONS = (".woff", ".woff2", ".eot", ".svg")
@@ -35,8 +35,8 @@ def font_dir_names():
 
 
 @pytest.fixture(scope="session")
-def formula_paths():
-    """All Formula/font-*.rb paths that exist."""
-    if not FORMULA_DIR.exists():
+def cask_paths():
+    """All Casks/font-*.rb paths that exist."""
+    if not CASKS_DIR.exists():
         return []
-    return sorted(FORMULA_DIR.glob("font-*.rb"))
+    return sorted(CASKS_DIR.glob("font-*.rb"))