feat: single-source theme discovery replaces three hardcoded whitelists

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

tests/test_theme_registry.py

@@ -0,0 +1,18 @@
+"""Theme discovery must be a single source of truth."""
+import json
+from pathlib import Path
+from app import core, theme_pro, theme_store
+
+ROOT = Path(core.__file__).resolve().parent.parent
+
+def test_discover_returns_builtin_themes_with_manifests():
+    ids = core.discover_themes()
+    for tid in ('automotive', 'industrial', 'corporate', 'minimal'):
+        assert tid in ids
+    for tid in ids:
+        manifest = json.loads((ROOT / 'themes' / tid / 'manifest.json').read_text(encoding='utf-8'))
+        assert manifest.get('id') == tid
+
+def test_three_whitelists_agree():
+    assert set(core.THEMES) == set(theme_pro.THEMES) == set(theme_store.BUILTIN)
+    assert isinstance(core.THEMES, tuple)