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

CLAUDE.md

@@ -161,6 +161,7 @@ Pytest settings are in `pyproject.toml` under `[tool.pytest.ini_options]` (`DJAN
 - **Name variables with complete words** — readable, unabbreviated identifiers in both Python and JavaScript (e.g. `template` not `tpl`, `event` not `e`, `element` not `el`, `removeButton` not `removeBtn`, `option`/`value` not single letters in loops). This applies to new code and to code you touch.
 - **Use `render_page()` not `render()`** for all full-page HTTP responses. Import from `common.layout`.
 - **Build UI with Python components** from `common.components`, not raw HTML strings or Django templates. `SafeText` children pass through unescaped; plain strings are auto-escaped.
+- **Prefer the named element primitives over raw `Component(tag_name=…)`** — use `Div()`, `Span()`, `Input()`, `Label()`, `Template()`, etc. from `common.components` instead of `Component(tag_name="div")`. Reach for `Component` directly only when no primitive fits (e.g. a bare, custom-styled `<button>` where the opinionated `Button()` would inject unwanted classes). Add a new primitive rather than repeating an inline `Component` for a standard tag.
 - **Filter views** accept `?filter=<JSON>` (structured) and fall back to `?search_string=` (free-text). New filter criteria go in `games/filters.py`; new criterion types go in `common/criteria.py`.
 - **Signals handle side-effects** — do not manually recalculate `Game.playtime` or `Purchase.num_purchases`; the signals in `games/signals.py` do this on save/delete.
 - **Button colors**: `blue` (primary action), `red` (destructive), `gray` (secondary), `green` (positive). Icon buttons use `icon=True`.