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/test_formula_exists.py

@@ -1,14 +1,26 @@
-"""Tests that a Formula file exists for every font."""
+"""Tests that a Cask file exists for every font with installable files."""
 import pytest
 
-from tests.conftest import FORMULA_DIR, get_font_dir_names
+from tests.conftest import CASKS_DIR, FONT_FILES_DIR, get_font_dir_names
+
+INSTALLABLE_EXTS = (".ttf", ".otf", ".ttc")
+
+
+def _has_installable_fonts(font_name: str) -> bool:
+    font_dir = FONT_FILES_DIR / font_name
+    for ext in INSTALLABLE_EXTS:
+        pattern = f"*{ext}"
+        if any((font_dir / "ttf").glob(pattern)) or any((font_dir / "otf").glob(pattern)):
+            return True
+    return False
 
 
 @pytest.mark.parametrize("font_name", get_font_dir_names())
-def test_formula_file_exists(font_name):
-    """Formula/font-<name>.rb exists for each font folder."""
-    # font_name is e.g. "font-acrylic-hand"; formula file is font-acrylic-hand.rb
-    formula_path = FORMULA_DIR / f"{font_name}.rb"
-    assert formula_path.is_file(), (
-        f"Missing formula for {font_name}: expected {formula_path}"
+def test_cask_file_exists(font_name):
+    """Casks/font-<name>.rb exists for each font folder with installable fonts."""
+    if not _has_installable_fonts(font_name):
+        pytest.skip(f"{font_name} has no installable font files (TTF/OTF/TTC)")
+    cask_path = CASKS_DIR / f"{font_name}.rb"
+    assert cask_path.is_file(), (
+        f"Missing cask for {font_name}: expected {cask_path}"
     )