Use element primitives instead of inline Component; add Template primitive

Add a Template() primitive for the standard <template> tag and export it. Replace
inline Component(tag_name="div"/"span"/"input"/"template") in search_select.py
and Pill with Div/Span/Input/Template; drop the private _template helper in favour
of Template at the call sites. Bare custom-styled <button>s stay on Component
(the opinionated Button() would inject unwanted classes). Document the
prefer-primitives convention in CLAUDE.md.

https://claude.ai/code/session_01XzhXvMvw42CQGc9kmin3GS

common/components/__init__.py

@@ -36,6 +36,7 @@ from common.components.primitives import (
     TableHeader,
     TableRow,
     TableTd,
+    Template,
     YearPicker,
     paginated_table_content,
 )
@@ -95,6 +96,7 @@ __all__ = [
     "TableHeader",
     "TableRow",
     "TableTd",
+    "Template",
     "YearPicker",
     "paginated_table_content",
     "GameLink",