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>

tap_cli/main.py

@@ -1,4 +1,4 @@
-"""add-font CLI: add or update a font in the tap, then run cleanup, generator, and tests."""
+"""add-font CLI: add or update a font in the tap, then run cleanup, cask generator, and tests."""
 import re
 import shutil
 import subprocess
@@ -7,7 +7,7 @@ from pathlib import Path
 
 
 def _repo_root() -> Path:
-    """Repository root (directory containing font_files/ and Formula/)."""
+    """Repository root (directory containing font_files/ and Casks/)."""
     root = Path(__file__).resolve().parent.parent
     assert (root / "font_files").exists(), f"Repo root not found: {root}"
     return root
@@ -44,7 +44,7 @@ def main() -> None:
     import argparse
 
     parser = argparse.ArgumentParser(
-        description="Add or update a font in the tap: run cleanup, generate formula, run tests."
+        description="Add or update a font in the tap: run cleanup, generate cask, run tests."
     )
     parser.add_argument(
         "path_or_name",
@@ -102,9 +102,9 @@ def main() -> None:
     if _run([sys.executable, str(cleanup_script), "--path", font_files_abs]) != 0:
         sys.exit(1)
 
-    # Run formula generator
-    formula_script = script_dir / "create_homebrew_formula.py"
-    if _run([sys.executable, str(formula_script)]) != 0:
+    # Run cask generator
+    cask_script = script_dir / "create_homebrew_formula.py"
+    if _run([sys.executable, str(cask_script)]) != 0:
         sys.exit(1)
 
     if not args.no_test:
@@ -114,9 +114,9 @@ def main() -> None:
             sys.exit(1)
 
     if not args.no_audit:
-        formula_path = root / "Formula" / f"{font_name}.rb"
-        if formula_path.exists():
-            code = _run(["brew", "audit", "--formula", str(formula_path)])
+        cask_path = root / "Casks" / f"{font_name}.rb"
+        if cask_path.exists():
+            code = _run(["brew", "audit", "--cask", str(cask_path)])
             if code != 0:
                 print("brew audit reported issues (non-fatal).", file=sys.stderr)